I personally would never give a mastodon community to a random individual if I had to step away. This is problematic on a privacy and operation level, not to mention the time it would take to interview people. Which means that if I didn't already have a second-in-command, the community would be shut down.
If it were a forum, then asking long-term contributors and moderators if they're interested in taking over is certainly an option. But it's not, there's likely no natural "hierarchy" that develops on a mastodon instance.
They could conceivably ask another established instance if they'd like to take over the old domain, though.