How do retirements affect a team's salary cap?

[FultzNationRISE]

If a guy retires at the end of the season, his salary clears the books right? But if a team goes and uses that new cap space to sign someone during the offseason, then the first guy decides a few weeks into the season he's unretiring... then what?

I'm not saying Lebron should or would do something like that this offseason, I just think it'd be interesting to know if, like, he COULD. Or you know, if anyone could.

Lebron does NOT need any more help. I'm just... curious if he could get it this way.

[Full Court]

As it stands now, Lebron needs three more retirements just to catch Jordan.