If I were a teacher, I would like to teach freshman English - so I could be the Robin Williams type in Dead Poets Society. I wanna be that guy. I couldn't teach seniors because they'd be smarter than me.
I'd never really thought past the whole dying-for-the-sake-of-the-world part of things. When you're alive, you don't dwell on how you're going to spend your time once you're dead. You just figure you're gone, and the rest will pretty much take care of itself.