What I understand is that the man resigned because he could not overcome his emotions. He did not use his head but rather decided to punish the management by resigning. This attitude does not work. Anyways, if he is regretting his decision, then he should contact his close associates or colleagues to trigger something that reminds management of his good work and contribution. Hence, a fresh initiative could be taken to contact him again to rejoin. This way, his so-called self-respect remains intact, and he regains his lost job. This will not happen overnight. It's time-consuming and needs lots of patience. The man has to maintain his cool.
I myself took a similar decision a couple of years back when I was transferred for no reason to an office 1800 KM from my city. It was a complete relocation. I resigned on the spot after a meeting with my senior. Though I was 100% right, I still relied more on my emotions. I suffered for a few months. My decision was firm not to rejoin again, despite calls from some seniors to resolve my issue.
Remember, every case is different, and the inside stories are difficult to understand.