I'm an old geezer. I don't like/use auto-anything unless I have no choice. For the past twenty years, I've shot primarily with a K-1000. By choice.
That being said, if the trip is going to be 6-7 months, and you're only planning on taking the 28-105 for the F-100, I'd choose the P&S. At least, I would if the trip were primarily a back-packing experience, not a photo trip.
1) It's probably lighter - not a minor consideration.
2) I assume that the zooms on the P&S and the F-100 will be about the same range, although the quality probably isn't as good on the P&S.
3) You're going to feel frustrated having a great body with only one lens. You'll want to get that long shot, or this macro, if only you had that lens with you, or the other one... at least, I would, over six months.
4) I suspect - but don't know - that the batteries will last longer in the P&S.
5) I suspect - but don't know - that I could stow the P&S in a ZipLock baggie to minimize the rain and dew. [Heck, I've even shot through baggies on stormy beaches.] Not so sure about the F100 & zoom.
6) P&S will have a flash for evening shots "round the campfire." [Are you still allowed to have a campfire?] While you might have a flash for your F100, you didn't mention it. And it's more weight and volume. (OK, OK - not much.]
But this all supposes that you're primarily going to hike and it's coming from an old (and tired and out-of-shape) geezer. My advice is worth what it's costing you.
Enjoy. I like your work; looking forward to seeing your trail pix.