Having a matched set of locks with one master key that takes 10 seconds to rekey is freaking amazing.

If so, just ask for the key and then rekey everything and take that out of their security deposit.  

You will be facing expenses to rekey the building so you have a master key.  

Make sure not to pay him until all his stuff is out and you have keys so you can re-key the place right there and then with a paper signed saying he relinquishes his interest in the property for X amount.

Hi, I am thinking of installing these electronic keyless locks to avoid rekeying fees for new tenants.

I asked her to call a locksmith and have it fixed, take a photo of the bill and I'd take it off their rent. 

Kwikset sells a Smart Key system that lets you easily rekey the locks in seconds.

If they have a key just re-key the thing.

Once the lender establishes that the delinquent borrower has vacated (correspondence with the borrower shows a new mailing address, for example) the property, then the lender knows that they will have to re-key and perform preservation measures - winterizing, board up broken windows and any openings, cutting grass, etc.

So, the property can be rekeyed and boarded, the grounds maintained, property winterized, repairs required to properly weatherproof can also be done, etc.