Mei uses hidden mist, obstrucking Sasuke's vision. He isn't doing anything from here on since he doesn't possess sensing abilities and sharingan can't see through mist. Gaara on the contrary possess sand sensing abilities, so he would have no problem to detect and catch Sasuke within the mist. Mei herself can probably fight in the mist without problems as well. While Tsunade herself can't see through the mist, she possess Katsuyu, that has sensing abilities as well, so she would have no problems to fight in the mist in this case.
A is the only one who would have difficulties, but he could rely on others to know Sasuke's position, on the contrary of Sasuke. Though, Sasuke could probably try to summon his snakes for surrounding detection, but against Gaara's sand or Mei's lava, they would quickly have to disappear. Tsunade can break through ribcage susanoo with bare hand(not easily though), so Sasuke would either have to stay inside Susanoo covered by enton or use the the complete one.
If he doesn't, he would get taken out by A's speed especially in this environment where he can't see. But even if he does, he still couldn't attack, and unless Kages are stupid enough to attack him in close combat while in this case, it would bring nowhere especially since they have long range fighters like Gaara and Mei on their side. Gaara's overwhelming attacks for example would be difficult for Sasuke to handle. Gaara is even the perfect one to be capable to counter him despite his Susanoo like he proved against Madara. So when Sasuke could do nothing against Kages in this scenario, the kages have plenty of possibilities to destroy him
The Kages have it on the bag, but it would depend if Sasuke kills Mei before she put up the mist jutsu or not. If he manages to kill Mei before, the 4Kages would still win, but with more difficulties. But Gaara is probably the most suited ninja capable to protect people while fighting, so a one-shot isn't that likely to happen anyway
