I don't think anyone likes characters dying, but of course the plot has to retain interest.
Of course since Richard Harris is already dead, They have probably had to replace him in filming already, (maybe with John Hurt?) and I can't imagine who they would have to take over Hogwarts in his place. He was reputedly one of the most powerful wizards around anyway, wasn't he? So I think that's unlikely.
I'd personally go for any of Percy/Peter/Hagrid if it has to be someone. It would be better if it were Filtch of course, but I'd go with Boy On A String and say Hagrid, since Robbie Coltraine was apparently making noises a while ago about not wanting to continue with the character I believe, so she could easily write him out I guess.
It'll be interesting to see who's right!