I never said anything about whether or not I would take someone's mob, or what someone's effort to create a pop set is worth (Lacovie is a bad example, it takes maybe 15-30 minutes depending on your luck to make a lacovie set via Gold Box since it's only 2 KI).
However, if everyone scatters and disengages to avoid nukes when they were engaged in the first place, yes, they will lose claim. People (should) know that. That is why, hopefully, they would not be attempting to use such a strategy.
For the record, it is perfectly possible to kite a mob that you have sole claim over while being greater than 30' away. You simply have to take an action against the mob after you have disengaged to reassert your "Non-Engaged" claim. Does Kirin go unclaimed when a kiter out-ranges a Stonega IV? Nope. Would Kirin go unclaimed if a DD who was the last person to hit Kirin turned and disengaged? Yup.
Yes, your intentionally extravagant scenario would result in an unfortunate loss for the party. However, it should not come as any surprise to them that it happened. Sometimes you have to make concessions in strategy in order to cement your claim on a monster. The point that I am leaping around is that all of the melee should not have scattered to the wind in the first place, as they would know that it could cause a claim loss.

