I’m just going to say it folks. If you’re always having issues with people leaving your groups in m+, the issue is following you. Perhaps some further analysis on what went wrong is in order. If it isn’t you directly as a player, perhaps it’s something unique to the groups you form like composition, or inviting people who are inexperienced.
Holding people hostage in groups that cannot complete the key by introducing penalties is a terrible idea. Depleted keys aren’t worth the time.