I am not all that familiar with Fedimint myself. but wouldn't what you describe apply to pretty much everything? We cannot provide a software solution to a hardware problem.

No matter the money form or technology, an armed band of bringands stronger than a community will always be capable of robbing them of things of value.

One can come up with elaborate schemes like time locks and temporarily prohibiting local access, but as long as you have access to people and you can coerce them to do pretty much anything. There is no money technology, that can fix that.

AFAyiK, it's a separate issue, that needs to be handled separately.