I think a "hopeful" open-ended conclusion is much more palatable in a book than on film. You invest a lot more of your time and emotion into reading a book, and the best stories always leave us wondering what might happen to our favorite characters next (if they survive) and part of the fun is imagining as your fancy dictates how such scenarios might play out.
Film -- particularly an adventure film -- is much more visceral and immediate, and its audience is much more likely (perhaps justifiably so) to demand that something "happen" to resolve the conflict and send them away sated. Fail to do this and you leave yourself open to charges of merely setting up the sequel . . . which is common enough in itself.
Frankly I think both versions are perfectly fine for their respective media and, while I don't regard either as anywhere near either artist's best work, I also don't think anything about either project detracts from the other in any way.