I personally feel that Percy will deteriorate far sooner than Mommy Dearest - it is already rather apparent. Then Mommy will become his caregiver, which, although she may have had some experience in being so in her previous life, it is not natural to her to do unless there is plenty of money involved. Who really knows?
Thankfully, I am certain that both Isobel/Percy's families with them marrying each other at their late stage in life, ensured that both of their estates were 100% legally separated and sewn up for the benefits of their own children etc. And, why not?
Well, that is what I would have done, no doubt about it!
If that is the case, Issy would then move back to her little house in Framlington, near her sister/BIL/Gerry for occasional support and that of the NHS. As far away from the madness of the HMN as possible, methinks!
However, what does appear rather strange to me, is that Issy really doesn't seem to have any friends - have I got that wrong? Maybe not so strange in reality, as she is defo not someone I would ever wish to spend any time with personally. Whatever, her life, thankfully, not mine!