pond crisis

Hi , I have had my pond about 7 years. I am in upstate NY with frigid
winters. Yesterday I had a major crisis. When I woke up the waterfall was
not working. I went out to look and noticed the pond had gone down about 8
inches (12X15---2200 gallons)
The Koi were in major distress, especially my largest blue one. He is about
2 feet long and was upside down f(. I assessed that there wasn't enough
oxygen in the water and proceeded to take the steps to correct it. I worked
furiously all day. About 2 in the afternoon everyone seemed to be stabilized
.. I thought I saw MR Blue swimming but I have not seen him since. I am
hoping and praying that he is still alive but if he were not would he float
to the top? How long would that take? Thank you for any help. Sofia of the
Pond