Charlotte waives and stretches Batum, the Celtics sign and trade Hayward to Charlotte with a second round pick, Charlotte sends Boston back a top 55 protected second round pick(which Boston never gets, by rule Charlotte has to send back at least that)
So Charlotte gets a free second round pick, and Boston gets a huge trade exception for sending out Haywards salary and receiving no salary back.
Above is the very-likely construction, and for the Celtics it's kind of a no-brainer to give a 2nd (or even 2 2nds that we just acquired) to get a $30 mil trade exception. That exception opens up a lot of options within the season and into next offseason depending on specific timing of the league year. Historically many TPEs are not used, and they already have a smaller one around $5 mil, but still better than not having it.
There's really little reason for Charlotte not do that, save three:
1) If they just dislike the Celtics (no reason to think this is the case, especially given last summer's swap)
2) If they feel, competitively, it is bad for them to give Celtics the TPE (seems unlikely given where both teams are) or hold out for a really high return and Celts won't pay
3) They are incompetent (MIL has failed to create a couple exceptions for this reason in recent years)
They also could loop a third team in should the rumors that Rozier is going to be dumped be true.