If it's not likely you will get the balance of the money, I reckon you should let him go on Saurday as you'll have a better chance of letting this month rather than next (xmas & all that). In fairness to him, he has advised you as soon as he could that his R/A was stopped.
I would view the property and deduct all appropriate expenses & any outstanding rent and return the balance (probably won't be amuch left at that stage). At least you have the opportunity to get it back on the market asap rather than trying to kick out a non-rent paying tenant for the next 6 months!