I've been mostly pretty forgiving of the writing choices on Castle for the last couple of seasons, and have kept watching despite the current showrunners' insistence on pursuing plotlines that highlight the weakest aspects of the series' writing. But this just boggles the mind; from day one, Castle has been built around the character partnership of Rick Castle and Kate Beckett, and I really don't see how the series can be realistically continued without both characters on board. One can only hope that ABC will put the fans out of their misery and choose not to renew the show.
For my own part, though, I actually don't think the mythology kerfuffles are as much of a disaster as the huge disservice the writing has done to both Alexis and Martha in the past couple of seasons. Martha has entirely lost her engaging con-artist's edge, and Alexis' original maturity and independence has been wholly forgotten in favor of turning her into "Alexis Castle, PI" (a role that exploits none of the academic, artistic, or personal interests she was shown to have while in high school and college). Indeed, the two characters have pretty much stepped into each other's original narrative functions -- Martha is now the mature, wise mentor, while Alexis is Castle's wish-fulfillment enabler and comic sidekick. It's pure good fortune that Susan Sullivan and Molly Quinn are sufficiently capable performers to sell their new roles, but it's a particular shame that we've not seen the truly brilliant young woman that Alexis should have become.
Ah, well. I foresee a hell of a lot of fixit fic emerging over the summer. And if anyone is still actually writing canon-compliant fic at this point, I rather suspect most of it will go AU after this season's finale.