Since the coach hasn't been delivered yet, it seems like one option would be to forfeit the deposit and walk away from the deal. However, since you aren't the executor, that's not your call. Of course, that option may not be workable if your relative paid in full in advance.
Assuming you eventually get title (or MCOA) for this coach and its already paid for rather than financed, there are two different strategies you could embark on:
1. Minimal effort on your part
2. Maximum dollar recovery
Minimal effort is to accept whatever the dealer offers for it (you can negotiate) or to turn the rig over to a consignment reseller. I'd work with PPL or other major (and reputable) consignment agent to get a credible estimate of a selling price and see what the selling dealer (and other local dealers) might offer for it. Be very careful of agents who merely promise high prices but can produce no track record of completed sales. There are a lot of those.
Maximizing the dollars requires personal effort to list the coach for sale in multiple places for max exposure and more than a little of your time and effort to take photos, send them to interested parties, answer questions, listen to offers (some of which will be off-the-wall), and fend off sales people who want to help you sell it (for a price, of course). And perhaps pay storage fees and a sales commission.