Fall of Guardia (Details of)
The principal, unknown variable in the future of Crono and Marle is the Fall of Guardia. The cutscene that ended the Playstation version of Chrono Trigger with their marriage was immediately followed by a scene depicting the destruction of the Kingdom of Guardia, set against the burning of Truce, the capture of the Masamune, and the slaying of the kingdom's final defender. Porre's new standing as a military power was confirmed in Chrono Cross, along with the downfall of Guardia, as mentioned in passing by Radius. What implications does the fall have for the two heroes? By marrying Marle, Crono apparently became prince (evidenced by his crown in the wedding). This established him as a member of the royal family, and perhaps next in line to become king. This fact verifiably anchors the two in or around Guardia as permanent fixtures of the kingdom. Secondly, we know that Guardia Castle was ransacked and that Truce (save for Lucca's house) was burned to the ground. Through Masato Kato, we also know that Crono and Marle might have been in some kind of incident during the fall, and that Porre probably had help from "outside the original flow of history." But these few facts are the only hard details known of the fall; even the fates of Crono and Marle are shrouded in mystery. We resort to theory to speculate on their destinties. How could Crono, Marle, and presumably Lucca, powerful warriors and users of magic, be defeated by the Porre army? What actually happened at the Fall of Guardia? Did they use swords or guns? Are Crono and Marle still alive?
Swords or Guns?
At the cutscene depicting the Fall of Guardia, we clearly see the last duel take place between two swordfighting men (one presumably with the Masamune equipped). The raging fire in Truce may have been caused by traditional fire weapons (e.g. Naptha).
Porre is shown to be completely oriented to using ranged firepower in Chrono Cross. Norris, the commander of the Black Wind, has also trained much of his life in using weapons, and the soldiers around Termina curse the outdated knights. The presence of raging fires in Truce at the Fall of Guardia cutscene may suggest the use of artillery or other modern incendiary devices. Nonetheless, fifteen years is ample time to switch weapons in the military, meaning swords still might have been used in 1005 A.D.
Crono and Marle Defeated?
This theory assumes Crono and Marle die in battle.
One of the most controversial tenets of RPGs is the death of players outside of battle. Characters who could take on an endless horde of enemies and are level 99 are nonetheless susceptible to death by plot necessity or convention. If we consider that the entire Porre army, armed with guns and cannons, assaulted the Kingdom of Guardia all at once, it is conceivable by plot convention that the heroes could be overwhelmed by ranged firepower. Guardia Castle would be shelled and the heroes would be might by a rain of bullets. This theory accounts for how the dated knights of Guardia could be defeated. Powerful beings in other stories are similarly susceptible to lucky strikes. One example is the Jedi from Star Wars, who, though possessing powers well beyond normal sentients, can be killed by normal means if unlucky or caught off-guard.
However, this theory does not jive with the ranged weapons of Crono and Marle -- their magic. Marle's Water attacks and Crono's Lightning could easily be used to attack enemies outside of personal combat range, and Luminaire could probably wipe out large portions of the army at once. Additionally, Serge and his crew face gun wielding enemies in Chrono Cross, and the battle system behaves normally (that is, they can use a sword again a gunfighter and succeed). Also, in another Masato Kato influenced game (Xenogears), the protagonist was shot by a revolver point blank and was only stunned. These problems cause this theory to rely on plot convention, which does not do justice to the strength of Crono and Marle. The one thing that might save this theory is Kato's statement about a force "outside the normal flow of time." This can be interpreted as a strong magic user from another era coming in to do battle, or a force of similar strength. Nonetheless, apart from the Gurus, Crono and Marle displayed power exceeding Queen Zeal, who was probably (apart from Magus or any historical figures in that civilization) the strongest magic user of normal history until the time of her death. Magus would have no motivation to effect the Fall of Guardia, which disproves his involvement.
It's also important to note that Crono and the others would have dealt with Dalton several times in the past, and may have considered him less of a threat than he really might have been. Dalton, soundly underestimated, could then strike with a surprisingly massive force.
This theory assumes Crono and Marle flee.
Perhaps the forces of Porre were able to turn the citizens of Truce against Crono and Marle. An anti-monarcy rebellion might have occurred in support of Porre's more modern and liberal state. The two regents, reluctant to fight and kill their own citizens, decided to flee when the invasion was staged. Lucca, on the other hand, might have accepted the change to stay behind (she has dealings with the Porre navy). This fails to take into account why Porre would ransack the entire city of Truce and slaughter civilians, considering under this framework the citizens would be on their side. It is possible, however, that the mysterious man who killed the last defender of Guardia was the doer of this deed.
This theory leaves their fate open.
Masato Kato noted that Porre had help from a force outside the normal flow of history. We can interpret this to signify that temporal attacks were used against Crono and Marle, akin to Lavos's distortions or the Entity's Gates. These would circumvent a pitched, magic battle.
Crono and Marle dead?
Given that Masato Kato states they probably were involved in some kind of incident, and that the lone defender of Guardia is shown being killed in the cutscene, it is logical to conclude that Crono and Marle were killed. Considering that in most governmental overthrows the former regents are hunted down and killed (compare to the overthrow of the tsars of Russia), Porre probably would have avidly sought them out if they fled.
Three things suggest that Guardia was able to rebound from this fall in 1005 A.D. Firstly, Radius speaks of Guardia as if it were still a sovereign nation. Secondly, Norris reveals when he approaches the Frozen Flame that Porre requires it to surpass the other strong countries of the world. Lastly, in the ending General Kid, Kid declares that the first order of business for the Dragoons is victory over Guardia, and then Porre. This suggests that Guardia did make a comeback, and that perhaps Crono and Marle are still alive and restoring the kingdom to its former glory.
Perhaps the most important evidence arguing for their continued lives is found in Chrono Cross; both pieces originate from Lucca. Firstly, in Lucca's orphanage, several drawings of Crono and the other heroes were made (perhaps excluding Frog and Magus). Considering that the drawings feature Kid, they were probably done after the Fall of Guardia, by the time she would be able to sketch (with other kids perhaps contributing with drawings). If Crono and Marle were dead, and Ayla and Robo had returned to their eras, how could the children know what they look like to draw them? One simple possibility is that the children used photographs. However, one drawing at the bottom of the wall appears to be of a Nu, suggesting that perhaps the heroes of time did visit one another (possibly through the Epoch, if it were not dismantled). Next, the second piece of evidence comes from Lucca's letter to Kid. Once again, its timeframe must be established. Since Lucca speaks of Kid's mannerisms, it had to be written after the Fall of Guardia (Kid would only have been one year old otherwise). Within the letter, Lucca speaks of her friends in present tense.
We still feel proud of the role we played in saving our world, and in how we were so freely able to change the flow of time.
I have had a constant dread in my heart that someone in our new future will travel back in time, just like we did, and try and kill or capture my friends and me.
It is certainly logical to assume that Lucca, when presently speaking of her friends, means Crono and Marle over Frog, Robo, Ayla, and Magus (since they have all returned to their respective times). This nearly confirms that Crono and Marle are still alive, perhaps in hiding or possibly assisting in reconstructing the Kingdom of Guardia (even if it is a derivative state of the larger nation of Porre). Only time and a new Chrono game will conclusively tell if they are alive.
From: Theory (Events)