No rule is inviolate
Epic is always good.That time the party wiped, was raised by a lich, escaped, then sought revenge...not that time the DM took it easy on us.
That blends with some prior ideas. Makes me thing of Ghostbusters where "crossing the streams" becomes the best option. We're all going to die but we're taking out the ancient god on our way. The backstory also blends into an ultimate BBEG that would lose a huge investment if the group's Baron dies. The rest the BBEG could care less about. She can't do a lot to intervene, but they've been seeing hints of her influence on these lands in the form of a very particular visual. If they see it again on something that helps in this place, of all places, it'll lead to a lot more questions than answers. Always good for a campaign."The lich is winning. Is anyone willing to be a martyr that the rest of the party can escape?"