4th Age Balrogs?

[Feanor of the Peredhil]

It's possible. At least, one escaped. Even though it said that during the War of Wrath all the Balrogs were destroyed 'utterly', one escaped, so two could have. Of course, with the current number narrowed down to seven, and three dead, that would mean that the Valar only killed two or less.

I think that was the only escapee, the Balrog of Moria. As for other warriors, nobody ever said what happened to the Hunter of Utumno, who ensnared the elves and brought them back to torture so Melkor could twist them over long years into orcs. Also, there were other demons besides them, like werewolves (of which in the third age Sauron had precious few), vampires of the like of Thuringwethil, and probably others. Not to mention the dragons that were still in existence. As for the Boldogs (I read up on them, don'tcha know), it mentioned right next to the name 'Orc Warrior', and orcs of course would still be around at least for a long while.