Plane engine paradox.. Predermined fate paradox..

There's an anomaly with the plane engine. It must fall through the worm-hole and not only kill Donnie to make the 'saving everyone' from the events in most of the film. Which means that the gym teacher, Donnie's younger sister (who's in the sequel) and everyone on the plane will die. Obviously Donnie's death would change what paths some of the characters take (or make, if it's not actually predetermined), but the engine can't exist twice. If it doesn't come off in the now 'fixed' universe, where Gretchen and Frank don't die and Jim Cunningham paedo-ring doesn't get brought to justice (bizarre for a happy ending), then it wouldn't be there to fall through the worm-hole. However, if it's Donnie who actually opens the worm-hole, then his death is another paradox. Although I think the ideas is that all the worm-hole and chest path things are supposed to be predetermined, which sucks. Just because (imaginary) Frank isn't there to sleepwalk Donnie out of his room, doesn't mean that Donnie with the knowledge of the future, can't get out of his room and still prevent certain people dying. The bottom line is, whatever happens in the events now that Donnie is dead, that plane engine must still fall off and disappear into the worm-hole, killing whoever is on the plane. In fact, the plane should actually crash killing Gretchen and Frank otherwise this predermined fate thing will also create a paradox, as outlined in remake of "the time machine" with Guy Pearce and even those Final Destination films, if Gretchen and Frank didn't die, Donnie wouldn't go back in time. I'm too confused now..