We might have evolved into a super-intellectual being by the time we invent time travel, and we're so smart, we can vibrate our molecules fast enough to disappear.

Or maybe, people do die, but they're living now. They won't be dead until we invent time-travel. Which we already did.

Next time you see a stranger, give him/her a second glance to make sure that it's not you. If you think it is...kill it. We don't want people from the future coming back and messing with us. Unless it's Sam from Quantum Leap.