PayPal does not provide seller protection for donations, so the donor could make a claim to the the donation reversed, so it would seem to be good business to accommodate a refund request for a donation rather than be subected to emails from the donor.
If there are specific threats you should contact local law enforcement.
As for re-opening, probably not, especially if it were a chargeback with the credit card. If the dispute were filed by the donor through PayPal, it may be closed permanently but that doesn't mean the donor can't open a new dispute with credit card.
Detaails matter.
