Is there any proof that Dr. Dehner won't be in the next Trek film?
There's no proof that anything will or won't be in the next Trek film.
That said, IDW is launching a series of Trek comics based on the relaunched Star Trek movies, with stories developed by the writers of those movies, which tell new versions of stories from the original series. First up is The One About Gary Mitchell
. It's vanishingly unlikely that they're going to burn that one off in a comic and then recycle it for the next movie.