Is it really? I've been reading over that chapter and I'm just not sure. I feel like it's potentially one of the weaker parts of the campaign. Blagothkus' reasons for helping the cult aren't all that convincing, especially given how easy it is to get him to betray Rezmir.The out-of-game reason is because Skyreach Castle is fun ...
It also feels like a TPK waiting to happen, if you run it without making any changes. Rezmir's pretty tough, as are the two Red Wizards. Then you've got a vampire with two vampire spawn underlings, which just seems like overkill, some stone giants and an adult white dragon. It really is a death trap. I almost feel like skipping it just to make sure that we *don't* end up with a TPK.
Plus, if I were to skip it, it would solve the issue of there being two white dragons (back-to-back no less!) in the campaign and no red ones.
I don't really want to cheapen character death any more than I already have, though.I can think of a couple of ways to patch it over. One is to let them get their resurrection more quickly than expected. Is there anyone left in the castle who might know exactly where some druids might be? Or what if a cult-aligned cleric/druid happens to come in through one of the portals--could they bluff a cultist into doing the spell for them?