Siam Ruby is one of the more cold tender varieties of banana. Your temps are way too cold. I would leave it in the pot, keep it on the dry side--60's should be mild enough. I do have some bananas in a cold garage (low 40's at coldest)--but these are cold hardier varieties (Chinese yellow, Basjoo, Himalayan, some dwarfs, Orinocos, etc.) Good luck!--P.S., You reminded me to check in on the bananas tomorrow.

Ryan

Siam is a tough one to overwinter,can you remove the rotted tissue?
As warm as possible would be best but it will stand still inside,
mine has been in a holding pattern since being brought in-the babies are moving though.

Good luck-I hope it makes it,my favorite banana plant afer Ae Ae!

Thanks for the feedback guys. I don't know if the roots are rotted yet or not, but I do know that 2 out of the 4 stems have completely rotted to the soil line and the other 2 are firm only up to about 8 inches high.

So if it is bone dry as I haven't watered it in months, should I water it when I move it to a warmer room?

Definitely water it if you move it into a warmer room. My banana plants drink a lot of water this time of the year (not as much as the summer) and even though I try to keep them dry, I end up watering them at least once a week (my M. velutina gets watered about every 3 days!).
Good luck! I hope it does well for you!
-Alex

If it is not active it won't require to much water.

How big is the corm/corms?

Hopefully it will remain dormant and spring into action in...
SPRING!

These are tough to keep going in anything but a g-house.

I put a plastic enclosure around my Siam,Rowe red and a
few others to try to keep the humidity/foliage up last winter...
it worked but the growth was very weak.