I'm not seeing a reason Yahtzee should be any different than any other game. Something may have gotten bugged when the game started or something.
If a player goes over time, you may skip their turn. With some exceptions, the rest of you can continue to play, but the results will be different. The skipped player gets 0 points and everyone else gets 1 and ties, and then ELO is given accordingly based on the percent through the game. So you have a 4 player game and you skip one player. The other 3 of you tie for the win, and it was 55% through the game when you kicked the player. You'll get 55% of the ELO you would have gotten had the 3 of you actually tied the game. Note that once a player is skipped, you can leave the game without penalty. Some people do this because the game is now missing a person and it's not really the same game anymore. Some games will not continue if you skip someone, like Hearts, cause it doesn't play 3 player.
You can try to do a group abandon. This is in the upper right corner. Just open that sometime and see what options you have, as opening it will not hurt anything. In this situation, everyone has to agree to abandon the game, except whoever disappeared. If they all agree, the game simply ends with no score, no ELO, no anything. There will be record of it but it says something like "undefined." Some people will refuse to do group abandons because it can be taken advantage of.
You can always quit, but you'll lose ELO and you'll get red thumbs and other players won't like you very much. I don't recommend that.
(Seriously, if you start a game, you're expected to play, at least until you get these situations resolved in some way.)
The best option, if you can't accomplish anything else, is to just let it go. The games end eventually on their own when turns are not being taken. (How long that takes depends if it's real-time or turn-based and the speed.) Just ignore it until it goes away.
Make sure that if you have a turn come up that you take it, regardless of what is happening.
If you don't, you'll be the one running out of time.