You can do so much with and OP staff in your possession than with money. 1st since there is reincarnation as far as we know there is no perma death for adventurers with status cards. Even if there is, as a gamer die grinding should be known to him. Go into the 1st floor and test what you can and can't do with the staff before deciding to sell it off.
If you can't dmg monsters with the staff by hitting them, then consider unarmed combat or joining a party as a temp healer with a mercenary as your guard. There are at least a hundred more efficient things a gamer would come up with than selling an OP end-game healer staff for a small amount of money (it would be worth way more than what he got).