Thor is the only factor here as he has ranged attacks that could possibly get through Mag’s EM field. The outcome depends on how Thor’s lightning interacts with Magneto’s EM field. If it can get through, Magneto would die. Thor can now instantly summon bolts from the sky, which could catch Mags off guard. If Thor’s lightning can’t get through, I don’t know who would win. I don’t know how much punishment Mag’s shield can take, so if Hulk or Thor get through that, Mags is done. Loki and Valkyrie would die to Mag’s projectiles, but Hulk and Thor may have the durability to take them. Also, could Thor’s lightning cloak shield himself against projectiles?
I’d say it would be a tough fight, and it’s split down the middle.