Yes, it is an interesting one. I think it hinges on whether the Letter of Appointment is in effect an excluded license.
The template LoA states “2.1 You should note that this Letter of Appointment does not grant you a tenancy or any legal interest or right of occupation in the accommodation.”
Given this, I don’t see how it could be perceived as anything else, in which case rent liability would end immediately on death. Anyway, I’ll let you know any further input that I’m able to get.