schala being drained of her power created TD and if TD was destroyed then all the different worlds created by the TD would disapear like nothing ever happened.
What?
No, that is not what happened at all, and if you listen to this person, ZealKnight, you are a fool.
Is that like where discarded timelines go?
In essence, yes. The Darkness Beyond Time acts as a sort of universal archive of destroyed or discarded timelines altered by time travel. Think of it as the Recycle Bin in Windows.
So, if A goes to January 1st, 2007 and alters X to X', the timeline that proceeded from X is transferred to the DBT, while the timeline that proceeds X' is the new timeline.
For instance if Crono had died nothing would be there, but because he won everything after that point was sent there.
I'm not sure exactly what you are referring to. Any changes made send the original timeline prior to the change into the DBT. That means that from the second Marle was blasted into the Gate in 1000 A.D. at the start of the game, all sorts of timelines were tossed into the DBT. We simply refer to the whole of the game as one timeline for ease of reference.
I read it in the encyclopedia, but could if there is only one then wouldn't be that after the unification all the lavoses would be thrown there thus he would fuse with all of them? (If that is a possability perhaps Chrono Break would use that to its advantage)
We don't know if there is only one DBT for all realities, or if each reality has a DBT.
Furthermore, what happened with Lavos has nothing to do with fusing with himself or what have you. Basically, the altered timeline in which he survived and spawned in the ruined future was tossed into the DBT after he was killed. Because he is such a powerful entity that he can affect time, he preserved the Lavos timeline version of himself in the DBT--or so one would presume, as otherwise there is no way he could have ended up in the DBT--and then he fused with Schala when she ended up in the DBT--possibly sent there by himself as a backup plan--after the new Ocean Palace Incident in which Crono and friends were participants. It is only the fusion of Lavos and Schala that created the Time Devourer.
Also how did freeing Schala unify the time lines?
Okay, first, one has to understand exactly what the Chrono Cross is. The Chrono Cross is a unification of the two Dragon Tears, one from each universe. It has the power to unify the dimensions when used outside of time, because it restores everything to a healthier state.
Given that Home and Another are interconnected in several ways unlike any reality seen in the game--through methods such as the character in your avatar, Turnip, who is a member of the Dream Species being dreamed up by someone in the other reality--they are really more like two halves of one whole, even though everything is copied. As such, they would be unified back together, restoring whatever harm to the universe was caused by the splitting. For all we know the splitting could have caused some gigantic tear that would eventually screw everything up entirely.
Schala and Lavos are two distinct beings who were being fused together into a new being. The Chrono Cross thus exerted its power to restore them each to themselves--Schala to Schala, and Lavos to Lavos. What happened to Lavos after this is unknown.
Just destroying the entity that was the Time Devourer would not be anywhere near enough to reunify the dimensions. It was the Chrono Cross that did so, and it could only do so outside of time, in the Darkness Beyond Time.