They did seem to (very strongly) imply that he was dead in Indy 4. But then he did drink from the Holy Grail, so if they want to bring him back, I'm sure they could come up with some reason to do with him having everlasting life (even if Last Crusade did say that it was so long as they didn't cross the seal, I know, I know!)
Still, Sean Connery doesn't quite look like a man with everlasting life, does he? He looks older than the 600-year-old knight in Last Crusade now!