Hey wkreps!
On our Super8's, the cvt gasket is a thick rubber gasket with a lip that wraps around the edge of the cover. The cheapest I've seen it online is about $15 plus shipping. The dealer wants $25 for one. The new mechanic there, who seems to actually know what he's doing, says it should come off OK. And it should be OK to reuse for a couple of times. But it never hurts to have an extra one, just in case.
As far as running without it, I think it's main purpose is to prevent metal on metal contact between the cover and the engine case. The cvt is not sealed from the outside environment. There's a vent at the front to allow air in to cool the parts, so if you are out in wet weather, it's getting wet inside anyway. Plus, the spot where the kick start comes out is open, so dust and crap can get into it anytime you ride.