1) I think that Prince Eric will only appear briefly in 3×6, since as the title suggests, this episode features Ariel’s story, and she may become a human only at the very end of the episode (if at all, since it could be in future episodes). I think Eric will feature more strongly in later episodes to come since his casting call said he was a reoccurring character. I strongly believe Eric is alive in the present-day but separated from Ariel; originally Adam and Eddy wanted to kill off PC but ABC bawked at this idea because that would’ve meant Snow White had no chance at her HEA and the same goes for Ariel. The network won’t stand for killing off Ariel’s main squeeze.
2) I think Felix and PP will live past S3. They’ve both survived in positions of authority for centuries which means they’re both skilled and adept at survival.
"That’s how you know you’ve really got a home. When you leave it, there’s this feeling that you can’t shake. You just miss it." Neal Cassidy