Okay, so I have this half-baked theory why we haven’t seen Kate at end-of-life for Rebecca, as we have seen Randall/Kevin.
I do believe, as was alluded to in gossip about show early on that they originally wanted Chrissy to lose a lot of weight. Then, that could show she “healed”, if you will, from her trauma as a child, not only from her moms focus on weight, but from loss of her father as her biggest fan.
How tragic would it be if her body finally looked like what her mom stressed about with her as a child, only for her mom not to know her when she saw her at end of life? Obviously, the other answer is she didn’t lose the weight, but has a wonderful life
I think her character is not going to be seen in flash forwards until it’s known how to write the ending for her character based on where the actress might be.
ETA: I say this even though I cringe at times folks focusing/making fun of her weight.