Layton, I think you're kind of being a dick. When I was doing SAR stuff, I can't remember how many times doing grid searches my team (I don't mean MY team, I wasn't a leader or anything) would just stop and lay (lie?) down right where we stood until the sun came up and we could resume searching. Granted, it wasn't "on route" or anything.
Even after joining mountain rescue and being on more "technical" missions, there were many times we would bivy in awkward places. Granted, they were also not "on route" but they were often in awkward locations (people tend to get hurt in awkward locations) and almost always in bad weather. For example, spending a cold night on a shelf at the Mt. Pugh saddle, above a subject who was stuck below, or a night in an awkward boulder field on Three Fingers while we waited to see if weather would improve enough to get a helicopter in.
Regarding the OP, instead of using a synthetic overbag, I would prefer a down bag that was warm enough (no overbag needed), and a lightweight bivy sack to protect against weather. If it was going to be an extended stay (rare in my limited experience with rescue), I would opt for a synthetic bag instead, and still use the bivvy sack. If you wanted to go lightweight, you might consider a down bag with an eVent shell -- I think Feathered Friends will make you one. Then, if it gets wetter, throw the bivvy sack on.
I have a mtn-hardwear bivvy sack that I really enjoyed, it has a see-through plastic window on the face (great for when you're in it and sitting up; you can see the weather or if it's daylight yet) and has openings for your line when sleeping anchored in your harness or just for venting.