I would say that its best to flush it now and just keep it in a warmer place if possible for a few days as continuing to grow in a soil with excess salts will only induce what Gabe said,continuing the damage to the plant. It surely isnt great to overwater with low tempratures but overwatering once for flushing the soil shouldnt be a problem if you return to proper watering regime afterwards. Keeping it in a warmer place for a few days after the flushing would ensure it will be perfectly happy with it!
Gabe has more experience than all of us probably with bananas though so i could be wrong but that works best with other plants after overfertilization and salt build up. It stops plant damage instantly. Of course then you need to watch out for secondary problems arrising from that damage such as damaged roots,etc but your plant seems in good shape and shouldnt be much affected.