You should count your fish on a regular basis to avoid that kind of thing. I appreciated how much patience is needed if you have a heavily stocked or planted tank but it's the only way of avoiding thiskind of thing and noticing if something's gone wrong early enough to prevent any further issues arising. In particular, if a fish dies in the tank, you need to be able to get the body out before it messes up the water.
If they've been jumping a lot lately, it's a sign something's a'miss.
I've not had a gourami jump under usual sircumstances but I have had gouramies leap from nets or out of temporary holding containers/buckets. None have died from this as I've always been there to put them back in the water before they dried up. I have, however, had other fish jump. In particular, the most recent occurance, was a zebra danio. She seemed to have jumped during the night or early morning and I assume it was while spawning because she had been releasing eggs on and off the day before and some plastic plants had actualy been knocked over, suggesting she was being chased and jumped to escape the pursuers. How she found her way out was pretty amazing though as the hole was truly tiny and not something I would have considered a threat at all.
If you're worried about the air, just get your typical wooden/plastic hood with lights for your tank. As long as there are holes for the various wires etc to come out of the tank, there should be air coming in. Also, if you have a bubblewand/airstone and it draws air from outside the tank, you're constantly introducing new air through that anyway.