You shouldn't have let them get this far without paying you in the first place. however since they are ready to move out, I would let them and make sure they don't cause any more harm to your house. Focus on finding new tenants now because November is a tough month. Think of it this way, they lived in your house for 5 years so that means you didn't have any vacancy for 5 years, $3000 over five years is not too big a deal. Next time don't let tenants owe you more than a month. Take action early.
You can still sue them after they are gone, but right now, you want them out without doing damage to your house.