Batch 1, Paid BTC, Canadian, and received an unsolicited USD refund cheque today.
Are you going to cash it?
I don't think he has a choice.
They're really fucking us over.
Typically a bank draft (Check) of which one is attempting to buy another off, in the case of a settlement, will be a 'Conditional Draft' (should have something on it to the effect of 'For payment of refund in full')
Cashing one of these types of checks will be viewed by the courts as an accepted settlement; a draft is a signed contract.
The flip side is if you did not request a refund, specifically have not provided them with any signed documentation to that effect and paid in bitcoins, then they just sent you a check...
Personally, I would cash it, then demand a refund of my BTC as per contract. If their accountant goofed and sent you a check in error, then they need to get a refund from you.
Does not your contract state to be reimbursed in BTC?
That would be fraud. You would have to first check with the letter as to what the intent is behind the check.
Two wrongs don't make a right and certainly don't strengthen anyones case.