I took a header into bottomless snow off to the low side of a sidehill from the main track last winter. If I had gotten back on the board and kept going downhill I would have just gotten myself into deeper shit, so the best option was to head back uphill. No swimming my way out of that one.
To climb uphill in the bottomless, I unstrapped both bindings, laid the board sideways in front of me (picture wings of an airplane) and held onto the bindings so my elbows laid on top of the board. I pressed down onto the board with my forearms to make a shelf of snow then did an ab crunch and flexed my hips to bring my legs beneath me (so now I'm balled up). I kept my shins close together to make as much surface area as I could, then lunged forward with the board uphill, then repeated this motion a hundred times until I got back to another rider's track.
It helps to:
1. Come to terms with the fact that you're not getting out of this situation quickly or easily
2. Keep breathing slowly and deeply as if you're doing a cardio workout, because you will be. Try not to blow up by going too hard in a panic.
3. Call or text your riding buddies (who are probably down at the lift line by now and are starting to worry) so they know why you're taking so long.
Good advice in there for sure, BUT, skip the phone call. If it's a sweet ass pow day, your friends don't care what's taking so long. They just care about getting in the next lap. Lol!