It’s an unfortunate occurrence, but it is not uncommon to have an owner in a keeper league bail on their team. Leaving all comments aside about how the guy is a loser for ditching, sometimes it really can be a challenge to find a replacement owner for an orphaned team, especially if the team is bad. This is an interesting rule variation I found on this site that could make up for that situation in some leagues.
A new Manager will have the option of keeping all x players from the team that they take over, but also has the opportunity to select half of the x from the remaining player pool (after the other 11 managers declare their keepers). This is to ensure that if a manager is leaving the league because they don’t like their team, the new manager has an opportunity to improve upon its given keepers.
Imagine you’re considering taking over a franchise in a 12-team league that allows up to 6 keepers per team. If the team you’re considering is full of bad players and the top 70 players (or so) are all kept, the chances of turning around the team any time soon are slim, so you probably wouldn’t takeover the team. But, give that same team the option to cherry pick from the best remaining players in the pool and the orphaned team could actually have an advantage, making it easy to replace the defecting owner.