Well, a LOA with PNCL unless medical, I don't see it happening. All they do is whine about not having enough FOs but off course, they won't hire more. Being an FO at the bottom of the siniority list in 9E is a nightmare. Remember, things are not moving, if you are on reserve, you'll stay on reserve for a while. If I had the oportunity you have right now, I think I'd take it. Never flown air ambulance before, but here's my reasoning:

Turbine PIC, hum..... good, very good
Pay, I'm not sure how much you'd be making, but for sure is more than 9E, isn't it?
Be based at home, hummm.....like it a lot
Job stability....either way is a gamble
Regionals are going to start hiring back again at some point, you'll always have the option to get your 121 experience, maybe even in a better company, a 135 or corporate gig is harder to get under those conditions you mentioned.
Being an FO at the bottom of the siniority list at 9E is going to get old really quick, specially now that the single most imoportant reason pilots chose to come to 9E is gone (upgrade time)
9E has nothing to offer right now in my opinion. Off course several regionals neither under these day's circumstances......

Anyways, remember 9E is a bottom feeder, and it'll always be, you are not leaving a top tier company....

Whatever you choose, good luck !