And what would the Balrog done later on? It's not like people went to Moria after Sauron fell (or did they?), and the only reason the Balrog was even out was because the Fellowship went through Moria. Do you think that the Balrog would have died when the Ring was destroyed? I would think not, since Balrogs were created before the Ring was.
Speaking of Balrogs, have you ever felt that it was Frodo's fault that Gandalf fell? I mean, if Frodo hadn't chosen to go to Moria when they were on Caradhras, then Gandlaf would still be there. That's just something I thought about once
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