Doubts about are Chichibu Festival plan during our trip

My boyfriend and I will be going to Japan from Nov 29th to Dec 15th and we noticed that the Chichibu Night Festival happens during our stay. We were planning on staying from the 2nd to the 4th in Chichibu but there are no places to stay on both days. Now our plan is to get to Chichibu on Dec 2nd and stay at a hotel that has a vacancy just during that night. Then on Dec 3rd checking out of the hotel  but leaving our luggage there so we can enjoy the festival during the whole day. Then, at night going back to Tokyo. My questions are: does this plan seem feasible/realistic? How easy is it to get tickets on the train back to Tokyo during that night? Do we need to buy them in advance? Thank you for your help!

by jcuadrado