This isn't a happy ending; look for yourself – Sandro, a great tactician and intriguer, really needs to return to Xeen, and for that, he doesn't care who he forms an alliance with, but he doesn't put too much effort into choosing allies. Besides, Lysander is a noble knight and won't betray a temporary ally prematurely.
Lysander also desperately needs to get to Xeen, but the only mage capable of getting him there and willing to form an alliance with him is Sandro. He's a little uneasy about allying with a necromancer, but he has no choice.
Kreg Hack – it's more complicated here; maybe Lysander and Sandro will capture him? But the alliance of life and death already existed in the campaign "The Succession Wars"...