I figured out the paradox of time travel wiping out whatever it is you came back to fix in the first place.

Self that goes back in time: Bob
Self that Bob warns of something: Fred
Self that Fred goes back in time and consequently warns: George

So its really simple actually. All you have to do is get Bob to go back in time and warn Fred about whatever it is you came to warn him about and tell Fred to go back in time on a specific date in the future to warn George.

See? Even when Bob disappears after warning Fred, Fred will still warn George no matter what happens because part of the warning was to go back in time to warn George about whatever it is that needs fixing, even if its in a future that is now perfectly fine.

Make sense?

-N