What happens to cards cast from exile?
What happens to a spell after it's been cast is not affected by where it was cast from. It's the usual rule about cards being by default "reset" whenever they move from a zone to another.

Unless the spell itself (e.g. Pull from the Deep, White Sun's Zenith...) or another card (such as Rest in Peace) says it doesn't go to the graveyard, that is where it will end up.