So, saddened by all of this horror, Donnie manages to travel back in time to the beginning of the movie and decides to just stay in bed and let the jet engine crush him, saving everyone else. The final scenes indicate that, with Donnie out of the way, everyone will live.
Frank goes on to a successful career as a massage artist.
Wait a Second ...
Or, here's another idea: How about not being crushed by the engine and simply using the knowledge gained in the "future" to prevent those deaths? Because we're not sure that dying fixes everything.
For example, if Donnie never burns down the motivational speaker's house, that means his kiddie porn stash is never discovered and he continues amassing his collection and working with children. If Donnie decides to use his time travel as a do-over instead of a suicide, a quick anonymous call to the cops could have taken care of that.
This might have been avoided completely if he'd taken Donnie skydiving.