It's not surprising Barbra survived the electrocution, because Diane survives, and Barbra has Diane's power.
The thing with Trevor possessing that guy is dumb, because at an absolute bare minimum, nothing comes of it. There isn't some sort of running gag about people recognizing him. Or some constant moments where Diana and Trevor are both aware that he isn't himself and it's kind of like... 'eh, maybe this isn't right' which would have helped push the plot of her giving up her wish. It is literally a thing for like one scene. It served zero plot purpose.
Also, it's not out of the question that Barbra kept her WW powers, minus the Cheetah, because she wished those against the Stone, and not Maxwell Lord, so when everyone renounced their wishes, including Lord, basically, the stone should have just reverted back to itself somewhere.