Hey, stop it with the spoilers for BEYOND season 3, lol! I didn't know anyone else was leaving. And did the actress who played Sybil choose to leave? I thought that was just a cruel plot twist that the writers came up with.
As for Dan Stevens... well, I can hardly blame him after some of the lame story lines his character was stuck with, although I loooved Matthew. I wish they'd given him a few more opportunities to do interesting stuff... like why didn't he, as a solicitor, help to clear Bates? He went to the trial to "interpret" the legal jargon for the family, that's all. And did he try to help Gregson find a way out of the legal trap he's in?
I DO blame Stevens for not agreeing to come back for just a couple of episodes in Season 4-- really, would that have killed him? (haha) Then they wouldn't have had to write him out so abruptly.