Of course, maybe Matt doesn't know what happened, Gail had an accident and hasn't been found yet. I've known several people (both male and female) who immediately start with the "my ex was a psycho" routine the second they break up, and maybe that's what Matt is doing and it doesn't mean anything more than he's upset his marriage was breaking up.
However, if she had an accident, my own personal problem with that scenario is that the vehicle hasn't been found yet. Also, it would be a remarkable coincidence that a woman as frightened as she was would disappear without a trace due to accident. Remember that there had been 3 911 calls because of domestic issues, she was telling friends and relatives she was frightened and she might be followed, she had receipts she thought were proof Matt was cheating, and she was giving papers and her passport and cash to friends to hold for her.
Changing her PINs and collecting evidence for the upcoming divorce doesn't speak to someone who is thinking of harming themselves, in my opinion. Those are the actions of someone who is planning for the future.
(I hope it's okay to repeat myself, because this is essentially the same thing I said a few days ago.)
The missing Jeep is troublesome to figure out under any scenario. The best scenario to explain is that is was involved in an accident in a very remote and rugged area or is under water. I think, in either case, she is with the Jeep.