The writer confirmed that he was able to move on and reincarnated meeting kanade's reincarnation. He will live a happy life see https://worldomonation.wordpress.com/2010/06/30/angel-beats-interview-with-maeda-jun-second-season/

According to Angel Beats! Interview with Maeda Jun, Second Season??, the writer confirmed that he was able to move on, reincarnated, and meeting Kanade's reincarnation. He will live a happy life.

Maeda was asked what happened to Otonashi after the last scene that moved many.

His response:

It was no use being there by himself, so I believe he also left the world after that. Besides, he was rewarded. It wasn’t a bad life. It wouldn’t be like Otonashi for him to stay. He’s a forward-thinker…looking towards his next life.

In the 3 days [between EP12 and EP13] there were probably a lot of drama too, but in the end, all other members left for their next life after a satisfactory persuasion from Otonashi.

So, for the TL;DR people:

Otonashi left the world soon after. In the 3 days he also convinced other SSS members to leave the world as well.