Very bad idea indeed :
- there are a lot of players who don't care about romances at all and wouldn't give a damn about any of fhe LIs dying. So the concept of a whole expansion about the loss of your LI would be quite boring for them.
- those, like me, who do care for the romance and their LI would be angry/disappointed and probably leave the game over this. We want more content with our favorite companions, not our LI taken away from us
To quote another poster :
If they kill my Malavai I'm out!