14d. Once plummy characters have been decapitated, gets back down to negotiating with the other side. (9) R?????G?S
17a. Linen starts to go out of fashion because it's widely regarded as an eyesore. (4) ?T??
20a. Vindicates in a rude or triumphant fashion, depending on what you can turn your hand to. (1,5) ? S???S