More than likely, Trigger was released purely for the need to gain athleticism in the post. None of Jawai, Loughton, Wotho or Trigger are athletic, and Wortho is the only half-way decent perimeter defender of the lot of them.
The reason it was Trigger and not Loughton would probably come down to the fact that Loughton has two years left on his contract, and Trigger just had this year. There may have been basketball related reasons, too!
The Snakes will be looking to sign (or are already on the verge of signing) an athletic 4 or 5 man. I can't see why they would do this otherwise.
I have very good intel that prior to signing Jawai, the club was looking at TWO "really good" Australian players. They are still looking for a point guard, a small forward and a power player, so it's possible it could be Bairstow. I doubt it, unless they have found a strong sponsor in a local economy that's pretty weak at the moment.
He will probably be replaced by a college grad from the US, I think. I doubt Burston will be back, unfortunately. He still has a lot of upside, too.