I think there are two things at play.
1) Breaking the DO curse and
2) Ensuring that Rumple lives
TLK will work but it is going to take more than that to break Rumple’s DO curse. Like I said a page back, I think it’s a mix of two things 1) Rumple choosing to try and break his curse with the ultimate sacrifice and 2) TLK
He has had TLK since magic was brought to SB (201, 222) but because he had not yet been ready to make the ultimate sacrifice, they didn’t break his curse.
Now he’s made that heroic sacrifice, but he has yet to be kissed. So both times he’s missing a key ingredient. And I think the large Rumple arc for S3B is him fighting against being controlled by Zelena because he no longer wants to be the DO and it’ll culminate in the TLK of epicness. And *that* will finally break his curse. And then S4 is about him trying to be a mortal man again.