I am not sure how something like is even supposed to work. After a licence of any sort is purchased, surely the sale is complete and payment non-refundable after a cooling-off period (if there is one) unless there is serious flaw in the software and the purchaser does not want to patch with any updates.
In your case, simply by returning a licence for a refund simply by asking for the company/website to remove a domain URL from their website does not seem like an appropriate reason for asking to get the money returned, it seems more like an attempt to get highly valued BTC given in lieu of removing the URL. If there is no legitimate reason or concern to return the licence why would you want to do it?
According to bustabit.com/license.txt there a total of 32 websites that are licensed to run Bustabit's software.
The problem, is that bustabit never actually provided a license. "Umm... Text file" doesn't cut it for real world situations like a serious buyer wanting to check in to things before making a purchase (Looking at the business revenue, number of users, gambling license, SOFTWARE LICENSE).
I have thought deeply about how to remedy this situation this last week.
I hereby call out Bustabit with this question publicly - For the integrity of Bustabit's name, and quite frankly, so people don't get scammed (Because the only buyers that readily accept "Umm... Text File" for a license seem to be ones that would use the purchase to scam others...) can a bustabit licensed website be surrendered (Domain control given to Bustabit & Domain delisted from the "license text file) to Bustabit for a refund of the original license cost (2 BTC) ? And if Bustabit isn't willing to provide a full refund for a product that was sold and never provided - is Bustabit willing to provide a partial refund and finally if so, what would the amount be that they would in fact provide for this situation ?