I'm going with "cease to exist", sadly, as no one reappears on the Valiant.

Harriet Jones: will definitely be called back to take over and govern until the next election at the very least (my own fanon, and honorh has kindly been writing a drabble using a line I suggested on the subject.

Lucy and the ring: no, not too large, but Lucy has read those UNIT files (well, some of them), remember. She has a pretty good idea that if she puts the ring on, she might end up out of her body for good, and that's not her idea of togetherness.