The people on the interwebs bitching about Matthew's death/killing are quite stupid.
Are they bitching about it? I'd have been totally surprised if I hadn't read frodo's post. Actually, I was still surprised because I had assumed that he was mocking us. Then when I saw Matthew tooling along in his roadster I thought, sonofabitch, frodo was serious. I guess I had not read that he wanted to leave the show. I hadn't read anything about any of these actors. To be honest, I'd not heard of any of them till this show, although I gather that many of them are quite popular in the UK. Nevertheless, if the actor quits you have to write his character out. Killing is a good way to do it, in my opinion, since it leaves no lingering doubts among the fans about any reappearance.
I have to admit to bitching about killing off Sybil. Especially the way they did it. It would have been easy enough to let her rot in a Dublin prison, or get kidnapped by the IRA, or even just have her stay on in Dublin because maybe she was too far along in her pregnancy to travel. In Matthew's case, you really don't have any convenient way to write him out, especially since they went to such great lengths to write him in. I think killing him off was appropriate.