Do the worker's dues lapse if the new sponsor refuses to pay them, stipulating their waiver in exchange for not transferring the sponsorship or for final exit from the country, knowing that selling visas is legally prohibited?

If you are entitled to financial rights from the previous contract, these rights do not lapse, and the partner who undertook to pay them is obligated to fulfill what he committed to. If he refuses, both of them can be sued. As for the visa, if it is only with the selling partner, he is obligated to pay your full rights, and the buying partner has no right to force you to work with him. However, if you fear harm from him, there is no sin in waiving some of your rights, and the sin will then be upon him.