Actully I think V_Translanka is a bit right in hsi non-sense.
I find IMO his attitude a little bit MAGUS-CAN'T-BE-KILLED->_<-!!!
but this spells seems really big, even for Magus. The only "proof" that I have is the fact that when Crono and co. shows up he doesn't say :"NO! please don't hurt me I must summon Lavos so I kick his ... hum shell"
he's pretty confident that his spell will work, but it doesn't and he blames it on the group.
In the Lavos timeline it was very different, Crono and co. didn't came so, maybe he summoned Lavos, if he did then he died for sure nothing to argue here (Imagine in new game + when Magus could beat Lavos 1 on 1 you start the game and no Lavos he died in 600 AD
), but if the spell was in fact too big for him he may have get crushed by it spells, got sent to anyother era except 12,000 BC (and where there were other gates). We have really no proof that Magus died, just that he wasn,t there after his Castle disapeared