Alright, this has kinda bugged me. We know from the Lavos Spawn in the first game that Lavos is capable of reproducing. Lavos can also apparently fuse with another powerful individual to create an entirely new being, as evidenced by the Time Devourer.
Assuming that other planets have individuals with magic similar to Schala's, does that mean that there could be multiple different entities similar to the Time Devourer?
Who said that was all it took?
The TD is produced by Lavos merging with Schala, no doubts there, but the Lavos in question isn't a Lavos from within time. That is to say, he seems to be the future of the undefeated Lavos. When Crono and Co defeated Lavos, presumably they left a dead body behind in the real world. But the future of that Lavos, the future in which it destroys the world, is relegated to the Darkness Beyond Time. The Lavos that merges with Schala is a Lavos that no longer exists.
Schala, on the other hand, may not be nonexistent. She falls through a vortex and ends up in the DBT. Is this because she's a Time Bastard? Probably not, as TB theory allows for there to be an large number of Lavoses and Schalas in the DBT. It seems, rather, that the real and present Schala somehow gets shunted to the DBT. The non-existing Lavos then merges with the existing Schala, providing an element of the merging that one just wouldn't get in the real world with a living Lavos. And, of course, the DBT places them outside natural time. It is much easier to eat a sandwich (that is, all of existence) if one isn't in the sandwich itself.
The TD thus seems to be only possibly if a Lavos is defeated by time travel, substantially reducing the likelihood of there ever being another.
