Sounds like fungus gnat larvae. They like to eat rotten banana corms. It probably had some other problem first that caused it to rot and they moved in to eat it up.
I'd take those pups you talked about off of that corm, take that corm and see if it's salvageable at all, cut off all the bad stuff and see if anything is left that looks like it'd grow. Let it dry out a few days, then dip it in a pesticide solution or at least a neem oil solution. Let it dry again and then replant it in fresh soil and in a different pot. That empty pot with the fungus gnats, either disinfect it thoroughly in physan 20, or a 1:10 bleach solution for 10 minutes or toss it out.
And those pups, check them for signs of the gnat larvae and also treat them with the neem oil or pesticide. That will give you the best luck, I'd think.
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