[user104658]

If he left and could explain his reasons and why he's now committed they would almost certainly take him back, they usually will unless the person has been discharged, because it's a bonus for them to recruit someone who is already trained rather than train a rookie. However, he would almost certainly have to go back in uniform.

That said, being in the police can be a very stressful / traumatic job (a good friend of mine was one and left because he couldn't handle it) and so to be honest, if his heart isn't in it any more, it would be a bad idea for him to do it (or to have carried on doing it) just because it's a stable career. It's not the sort of job you do just for the money.