Wow I've been out and come back to these shocking news!
Firstly, Henry was an amazing Geralt and for me pretty much the only redeeming thing about the show, his clear passion for the The Witcher books and games was the glue that was holding this mess of an adaptation together, I remember when he mentioned in an interview he convinced the writers to change Roach's death scene in the second season which was originally meant to be a comedic moment... He also talked numerous times about wanting to respect the source material because he is a fan and he knows fans like him are watching in the hopes they see a good adaptation, season 2 already proved that a "good" adaptation is not in the cards for this.
Him reprising his role as Superman definitely played a part in this but I believe it mostly came down to the fact the writers working on The Witcher show despise the books and games as it's been officialy confirmed by a former writer who worked on the show, I've no doubt Henry could've juggled Witcher and DC with Netflix even delaying the show to wait for him, the fact that it seems like that might not even have been discussed makes it pretty clear to me that Henry himself ultimately made the decision to leave and I don't blame, the show feels cheap, most characters are horribly miscast and I never felt chemistry between Geralt and Yen nor the family dynamic they are supposed to have with Ciri from the few scenes they had together, that dynamic is supposed to be the heart of the whole franchise and it just doesn't work with the 3 actors.
Liam Hemsworth is in a tough spot, I don't wish him ill but I never found him a good or captivating actor he certainly doesn't have the charisma and gravitas Cavill has and even without the comparasion I find him a horrible casting choice for Geralt but I suppose Netflix and the writers want to keep the tradition of horrible castings.
All in all it sucks Henry is gone but I'm not too heartbroken since the show itself has never been that good, Netflix should've just cut their losses and cancelled it or made a deal to close everything out with a small run of episodes or a movie with Cavill because this will crash and burn after he is gone and it's only right after hearing about how the creative team has zero respect for the source material and us and Henry, actual fans who just wanted this to be good.