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.

When mastodon.technology shut down, the operator commented on this, see "Why Not Transfer to a New Admin?" here -- https://ashfurrow.com/blog/mastodon-technology-shutdown/