Since there's no way out of it, once in, I'm inclined to say the player forfeits all future turns, meaning the other player can play on auto-pilot, which most likely will lead to their win.
This sounds reasonable to me. The wild card is designed to allow you to get out of this situation once.
An alternative might be to sell a single card at face value or half value. I think I would only do this when playing with kids since they tend to like to play out the game.