Lady Rapunzel wrote:
So... was Adelaide's exit her own choice or the writers/producers? Any evidence about this?
A mixture of both, probably? It was stated that Drizella, Alice, and Tiana all had the potential to be promoted mid-season; obviously, that went to Tiana. My best guess as to why is that Mekia Cox would be busy on Chicago Med, so they gave her the bigger salary so she would clear more of her schedule.
On one hand, Drizella seems like the kind of character who would stick around until a potential Season 8 as the "redeemed villain" stereotype (seeing as there were few options for that, besides maybe Samdi). On the other hand, the style and timing of her exit didn't seem particularly out-of-nowhere. She resolved her issues with her mother (more-or-less), Henry, Regina, and Cindy, and they needed a way to keep Anastasia safe so that they could switch the focus of the Guardian plot over to Alice. Drizella was the most logical choice to do that.
It's possible Adelaide Kane didn't want to stick around for the whole season if she wasn't a series regular; it's possible the writers changed their minds after promoting Tiana and elected to write her off as a guest star. Whichever one it was, I'd say both parties had plenty of warning to make plans (Adelaide knew when she would be done and didn't seem too surprised; the writers were able to write her off satisfyingly instead of suddenly), indicating the parting was amicable, so I don't think it matters.