Warning: do not read if you really don’t want to be spoiled OR if you’ve avoided MAJRO spoilers I don't think Tamara or Greg will die because they kidnap Henry and take him (we think) to Neveland before the Charmingstiltskin clan follows.
We don't know at which point in the episode this happens. It's been said that the prophecy of Rumple's undoing will play this season, and I can't be the only one thinking its twist is that it's about Greg and Tamara forcing Rumple to choose between his life or his grandson's. In this scenario, I can see Rumple finding a way to save both him and Henry as well as giving Tamara a death we won't forget.