It is simple maths to know where the open end of a snorkel is. Generally people are vertical in the water waiting for the boat. The snorkel generally sits at 45°. Let’s say the snorkel is 30cm from the mouthpiece to the open end. This means the open end of the snorkel is about 20cm higher than your mouth. Although I don’t have it clipped to my mask I do carry one.If by some happenstance I'm floating around for 10 hours on the surface, and I'm so delirious that I'm face down, there's no way I'm in a fit state to use a snorkel safely
If I'm face up (and why would I not be) then I'm perfectly capable of closing my mouth to avoid inhaling seawater, and taking breaths as normal between waves. I know where my mouth is, but not where the open end of a seawater-collecting head-straw is.
IMO a snorkel is an oldschool useless piece of kit that solves no problems, except possibly if I need to swim somewhere quickly using front crawl - for example escaping a great white after I've failed to kill him with my oldschool BFK!
I have never been in the sea waiting to be rescued. But have dived with people who have spent hours waiting to be rescued, and they did use their snorkels.
Going back to the OP. I would keep my second stage in. With a 50 bar reserve there should be enough for getting on for an hour.