Ralph, I'm also airplane and rotor-rated. The "beauty" of a forced landing in the heli is the small area that you can put it into, as you know, compared with several hundred feet for a fixed-wing. Of course, we all know that the aircraft doesn't know it's dark, and is no more prone to failure. The risk isn't in the A/C quitting, but the consequenses if it does. Night crashes have a much higher fatality rate than day.
Autorotating to the ground shouldn't be terribly risky, unless you can't see it. That's the part about night flight in the heli that bothers me. At least in a FW, your rate of decent might be 400-500 in a lot of typical SEL, and if you have any chance at all to flare a little, you're not going to hit the ground too hard, although you might hit an obstacle in front of you, of course. When the heli is coming down at 1500 FPM, it's bad news if you don't get to flare in time.
From my reading, it sounds like fast collisions with the ground vertically result in some bad back-compression problems, whereas in the FW with higher groundspeed and lower ROD, your speed most likely will be dissipated more gradually, meaning less serious injuries. Both are unpleasant to think about, but if it's particularly dark, or over rough terrain, I think I'd prefer crashing in the 'plane. However, if I was a more experienced rotor guy like you, I'd probably change my opinion.
Many years ago, when I gave my first safety talk as the new Safety Officer in a state pilots organization, it was October, with Daylight time about to expire. I gave many tips about night flying, the last being the old saw about a forced landing: "Right before you get to the ground, turn on your landing light. If you don't like what you see, turn it off." Funny to talk about, but I hope to never be there.