Board Thread:Suggestions forum/@comment-26119768-20170222024948/@comment-31907131-20170222075601

Recneps wrote: I've always thought that an infinite amount is just fine. It's rare to see more than 3 at once.. And we know that there were at least 7, and very probably quite a few, Balrogs in existence. They were Maiar, and Maiar tend to be immortal, even if they can't take form again easily.. I picture the slain Balrogs fleeing and then recuperating in this ruined stronghold, which presumably has some leftover magic from Morgoth. But you can, theoretically, keep finding and slaying Balrogs... and certainly if there were seven or around that number, there would not be three left aside from Durin's Bane at this point. Ecthelion killed Gothmog, Glorfindel slew another.

And get this tasty quote, from Tolkien Gateway:

As the legendarium became more formidable and internally consistent, and the Balrogs more terrible, this number was much reduced. In the end Tolkien stated that there were probably "at most" seven Balrogs:
 * "In the margin my father wrote: 'There should not be supposed more than say 3 or at most 7 ever existed.'"
 * So no, as this was Tolkien's later opinion, not at least 7; at most 7. Recuperation? More likely after their death their spirits would return to Valinor, and from thence be cast into the Void like their master Morgoth. The one reference from which the Balrogs in Utumno were probably derived was from the First Age I believe, when Morgoth called for aid against Ungoliant and the Balrogs who still dwelt in Utumno after his first defeat answered. But the problem with this is after his return to power, the Balrogs came to Angband, which became his new stronghold until he was finally overthrown. All the Balrogs left at this point likely perished in the War of Wrath or were captured at the same time as Sauron and Morgoth, except Durin's Bane and perhaps another couple of exceptions.
 * So there is a more accurate representation of lore, my friend.