Does Anyone Have a Crafty Idea to to This?

If the plastic is strong and can withstand the ripping out of the zipper's stitching, and if you can take the whole thing apart enough to fit it in a sewing machine, you could consider reinstalling the zipper with a different starting point. It sounds very difficult though, even if the plastic wouldn't rip. I vote for Margie's velcro solution. I imagine you'd have to attach some tabs or a long strip of something so there is overlap and the pieces of velcro have a way to stick to each other. Take a photo (or 3 or 4 - one overall plus a few close-ups) and take them to a good fabric or craft store to see if they have a recommendation.

Or just replace with some strips of non expensive velcro. You can pick that up anywhere. You just zip it up to keep the heat in, but if it's not zipped up perfectly, I'm sure it would be fine.

I'd probably take the lazy way out and forgo the zipper using velcro instead.

Only way you can reverse the zipper is to take the zipper out. Reverse the zipper and reinstall it by top stitching the sides onto the zipper. This doesn't require much skill since the sides have already been prepped for the zipper. If you can't do this, any seamstress could do it for you.