First off, Americans, I'm not talking the Boston Tea Party, here.
Think more along the lines of the Mad Hatter's tea party.
I was imagining the different approach we take talking our loved-ones, depending on whether they are in their cult mode or natural mode. I've said often enough, address the natural person, and keep the cultist calm. It can be distressing, for instance, for a daughter to watch her natural mother subside in to the background, to be replaced by this plastic stranger. How can the daughter keep the pretense going that she is even comfortable around the replacement?
Imagine you are going to a tea party.
The manners, conventions, and behavior are all laid out ahead of time. You know the role you are to play. Keep the conversation in bounds with convention, and nod politely. Give no sign to the cultist that you aren't perfectly happy sitting there sipping tea. If you're not sure what this is supposed to look like, look at the plastic families profiled in the magazines, or a role-play demonstrated at a midweek meeting. If you are offered doctored kool-aid, politely refuse.
Take comfort that there will be another day when you can conjure forth your loved-one again, by reminding them of everything that makes them special and unique.