Yes, it can happen as I found out
They didn't bother jumping out when they spent two months in an open top plastic container 30cm tall or so while I was transitioning tanks....They don't normally jump and I was relying on that, the fool I am...
What bothers me is that he jumped out of the side where I feed them. Its a round tank so he could have jumped out any side but I found him right in front.. I dropped food in the morning just before I left from the same side. I normally feed them when I get up and if he jumped out because of excitement for food, I may had been there....Once they nibble all from the substrate they normally come back and start begging for more. It must have happened early as he was long gone when I came home.
He was chunky and fat and a relatively fast growing loach. Also, because he was younger, he also ventured out a lot more often than his older companions and stayed with the baby loaches who are out all the time, and this could have been another reason for him to launch out. The water level is never up to the top, so it must have been a big jump.
This is one of the times I wish I could turn back the clock and re-live it again