What I disliked the most about his situation was they completely destroyed Toph's character because he didnt want to sign for an 8th season. It all went to hell when he was approached for a 7th season. See he and Ash signed up to s6 like someone upthread said and both Ash and Toph wanted to move on. Some of the cast/crew took that personally and I believe one of them went to the producers. Toph signed last and said no more than s7. Long story short Mark (who was featured a lot in THS) didn't take this well and completely taking it out on Toph's character. They treated him like crap and BSed their way thru the True Hollywood Story. He ONLY returned to close out his character in the series finale with two conditions. They abide to his other contract S3 and that he would didn't have to do the live show, just pretape his scenes. So how that whole he wasn't there for the finale worked out for THS is because truthfully he wasn't there BUT he was there for the wrap party.
Not sure where you're getting any of that. None of that was ever featured on the THS, unless they've completely changed it in the last few years. If Mark is Mark Brazill, I know Topher just did a movie with him (Take Me Home Tonight) so there must not be that much bad blood between them. I don't really see where they treated him like crap either, obviously Eric and Donna were going to have to be broken up.