(Higurashi spoilers) Well, I never really got the impression that Bern was booted out of Rika against her will in Saikoroshi. For example, let’s look at the Frederica Bernkastel personality before she split from Rika.
(Higurashi Kamikanshi spoilers) [spoiler] Rika in Kamikanshi is so much like Bern that I’ve joked that Ryukishi wrote so much Bern in Umineko that he forgot how to write Rika. Rika in Kamikanshi only cares about two things: being amused, and winning. She couldn’t care less about her friends (not even Satoko).
This is the side that I think split off from Rika in Saikoroshi. So it seems unlikely that she’d be happy living a peaceful life with her friends. (Not that Bern is terribly happy now anyway.)
This would also fit with what Ryukishi said about Bern being the evil part of Rika. [/spoiler]
Or at least, that’s how I see things… I could be completely wrong.