He's got plenty of leverage, assuming that the product is a part of the company sale pitch, i.e. the company is not being sold just for its customer list, websi

He's got plenty of leverage, assuming that the product is a part of the company sale pitch, i.e. the company is not being sold just for its customer list, website rankings or other non-product assets. Edit - looking through OP's commenting history, it appears they are working on the real estate market software. In this case it is very likely that the company is being sold for the list of its customers to a larger competitor, to allow migrating customers to the competitor's platform. In this case the OP has little to no re-negotiating power, because the product is not what being sold here.