The fact that Regina had Belle locked up all along and had led Rumpel to believe she was dead is probably more than enough for Rumpel to want revenge without adding Belle’s death on top of that.
Just thinking back to Regina’s and Belle’s conversation in Skin Deep, makes me wonder, did Regina know who Belle was even though she had supposedly just met her?
I can’t remember Regina’s exact line but it was something like: “I would never suggest a woman kiss a man who held her captive. What kind of message is that?”
How did Regina know Belle had been taken by Rumpel as payment and was she actually hoping Belle’s kiss would take away Rumpel’s powers? How did Regina know the kiss would even stand a chance of working?
All magic comes with a price!
Keeper of Felix