Come to think of it, has In Flames ever fired a band member, as opposed to those members leaving of their own volition? I know Dark Tranquillity hasn't been afraid to kick people out before.
I can't think of anyone.
There's been some speculation whether Jesper was kicked out, but some months ago I read a Swedish interview (from 2012 I think) with Peter and Björn where they touched upon the issue. They were asked how did the discussions about Jesper's departure go. They said as they were completing the ASOP tour without Jesper, they were hoping that he would seek help in the meantime, but after the tour was finished it was clear he hadn't got any better. Then the rest of the band started talking about it and came to the conclusion they cannot any longer afford to be in a position where one can never be sure if one of the guitarists is able to perform or not. However, they didn't want to kick Jesper out, "especially him being the one who started the band in the first place." So they were planning to give him an ultimatum, to tell him "Look, you cannot be in the band if you drink that much. You need to get help and bring it under control. Or otherwise we have no other option than to ask you to leave the band." They were hoping it would trigger a reaction in Jesper, a reaction like "Oh shit, if I don't shape up I might to have to leave my own band!" that would motivate him to clean up his act. But before they could deliver the ultimatum Jesper announced he's quitting.
As for the rest...
Early days guys who came and went Stanne, Forss, Anders Iwers, Näslund were only session musicians.
Johan Larsson quit playing bass altogether.
Glenn wanted a "normal" job with fixed income to provide for his family.
Niclas originally left because he was too busy with his other band Gardenian at the time.
Daniel left because of family reasons.
Peter left because he was done with the whole touring lifestyle and wanted to do something different.
Joe Rickard had some back problems I think, and preferred not to do long tours.
Then there was some Swedish bassist called Håkan, was he meant to be a just temporary replacement?
(Did I forget someone?)
Of course, based on what Peter and Björn said, had Jesper not left on his own accord, and had he continued to be unreliable, it's quite possible he would've been ultimately fired.
EDIT: Added info on Niclas.