Some say Miguel is Crono too.
For me, I think Crono died at the Fall of Guardia. You're right, we don't know for sure, but I just think it happened that way.
Also, something else: I thought ALL the inhabitants from El Nido were either workers from Chronopolis or descendants of those workers?
If that is the case, there's no way Crono is around. Or any other character we knew from Chrono Trigger. (Of course, the "Ghost" Children, Schala, and Lavos are exceptions, but Schala and Lavos aren't in El Nido and the Ghost Children don't really exist.)