I guess, in my mind, the question is more focused on does Leia really need to be in the story anymore? Why not just say that the death of Han at the hands of her son caused her to leave the Resistance and disappear out of grief?
Han seemed like he was supposed to die in Episode VII, and his death added a good amount of weight to the story. However, I would not have been in favor of his being killed just to explain an absence of Harrison Ford. There are plenty of other ways to do that. Killing off a member of the original Falcon crew gang should be done with care and mind toward telling a good story, not just to explain their absence.
Think how tonally weird it would be to have Leia be killed offscreen or via a hologram in the original trilogy. If they had done that to Han Solo or Luke Skywalker in Episode VII people would have rioted. The only reason why it seems like a good idea to you guys now is because Carrie Fisher just died less than 24 hours ago. It would look sloppy and be a really underwhelming end to one of the best scifi women ever.