SickChill won't be removed anytime soon.
I need to do some testing and see if it's possible to transfer the database across to other SickBeard forks. I'd like to avoid having to rebuild entire libraries of shows from scratch (although importing existing shows should be quite easy these days). I hope to find some time this weekend, but there's no hurry. We have a working SickChill for-now: it just won't get any further updates.
I hear you, and it's painful when I have to remove an application. Frankly, I don't use sherpa at-all, as I don't run QTS on my production NAS.
The sherpa installer might be best-seen as an "easy"(?) way to install some difficult apps and get them running (I remember how difficult all this Usenet stuff was for me when I was first exposed to it, and trying to get the planets aligned by ensuring all the applications worked together wasn't a great experience), but the longer term view should be that the user runs each of these apps independently of sherpa.
So, outgrowing sherpa is a perfectly normal progression.
Maybe someone who has compared each of the SickBeard forks can comment? I'll admit, I've not used the other forks in a production environment so I'm not intimately familiar with their differences to SickChill.