Your main objective here is to regain your property in the best possible state
Tread carefully until you get the keys back and they have left.
Be prepared to write off your lost rent.
Try and get a forwarding address. (Say in case you get an important letter for them)
Maybe suss out how strong the guarantor is.
Maybe a debt collector will have a go and chasing it for you
If you have an insured deposit maybe leave it three months before closing it off, proving damages can be a pain
Personally I’d have been onto the guarantor a day or two after the first payment was missed, if I hadn’t heard both a reasonable excuse and a proposed (near) date for payment.