I’m not sure about that. Sure, they have to sacrifice “the thing you love the most”, but does that mean death? Regina could cast the curse in 3×11 because she sacrificed Henry. She didn’t kill him, but she had to accept that she would never see him again. That’s been a huge sacrifice for her (the one she loved the most) too, without killing somebody!
That version of the Curse was set in motion by Pan killing Felix. What Regina did was in response to that, but the actual Curse was happening at that moment because Pan sacrificed Felix.