It's possible Charles is our last role, but if he were the watcher, I think he would have checked Joshua over the Doctor or Lithuania. Whatever the missing role is though, it either hasn't taken effect yet or isn't that big a threat. They need to get rid of the watcher first.

The two Hope's Peak kids will be in trouble once the town start questioning why Kirigiri is still alive, especially Togami and his odd voting history. But as long as there's no investigative role left, we may still have a good chance with the remaining.