Please don't take this as a cop-out, but I would strongly recommend that you call OFAC to get a specific answer regarding the scenario.
My understanding from past conversations with OFAC is that where the accountholders are physically located could determine how you are permitted to go about closing the account by check. I also understand that, regardless of where they are located, you can close the account and wire the funds to the accountholders to a non-US (and non-OFAC-sanctioned country) account.
Although it can sometimes be frustrating to try to reach OFAC, I have found them to be very helpful in answering questions about the do's and don't's for those confusing country sanctions!