Serve the hoarder with a non renewal and get rid of him. No reason to ever hold on to bad tenants. Plenty of good tenants out there waiting to move.
You will need to likely evict and then renovate to repair damage. Better sooner than later before the damage gets worse. If he refuses to leave get the building inspector and fire marshal to inspect and declare the unit unsafe for occupancy. This will assist with your eviction. Once you get him out and reno you can easily get the declaration lifted and re-rent.
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