It's just cheaper to raze the buildings thn resotore them. I would hope they save whatever they can, but probably not. Whomever gets the demo contract will have a treasure trove, but probably won't realize it. The NPS is really hurting and not just at the DWG NRA, most of their infrastructure is in dire need of repair, the same can generally be said for NJ state parks. That won;t change anytime soon.
Not sure where you mean, the only road I know of that crosses the LFB is Ennis Rd, which has been closed for a very long time due to the bridge washing out. Do you mean the bridge just downstream of the LFB that crosses the BFB, a spot where trout fishers park? It is right off 615 and connects to MT Rd/Brook Rd.
The only other bridge on the LFB is on 521 up at Layton. There are two bridges (I think) over the BFB that are closed, so perhaps JG is referring to one of those. There is Bridge Rd., just south of Bevans/Peter Valley, and then a little further south Fish and Game Rd., both of which cut from 615 over to Mountain/Brook Rd. The two that I'm aware of that are open are Main St. bridge in Wallpack, and the one connecting to Haney's Mill Rd.
As far as a "treasure trove" is concerned, there is definitely some value in some of these old properties, but I have been in almost all of them over the last few years to take pictures, and there ain't a lot left in most cases. Of course, with some of the older properties just the beams from the barns would be valuable, but in terms of hardware, artifacts, etc., anyone looking for that kind of thing will largely be disappointed, at least with the properties near the public roads. There are a couple of places more off the beaten path that might yield things of interest, but not of much value. For example I have found a reminder for a Dentist's appointment from the early eighties, and a copy of the NYT from the seventies. Not much value, but interesting nonetheless. I leave everything where I find it (well, save for one railroad spike filched from the Lackawanna Cut-off, to which I plead guilty), so those things are still there to be found, anyway.