LotR Gregor: If you use his any phase action, and someone saves the target from being killed, does gregor still stand?

Nope. The use of the word "Then" is important. In order to stand him, the preceding action must have been successfully completed, i.e., the character being killed.

i understand that. the debate we had was this. we both agreed that if the kill was canceled, that he would not stand because the kill was canceled during initiation. saving however isn't canceling the effect, the effect is happening, and the save is reacting to it rather than preventing it. we both agreed that an argument could be made for both cases quite logically (as so whether he would stand after a save).

As far as my understanding goes gregor need a character to actually hit the dead pile to resolve, the save essentially cancels the moribund state: dead pile and keeps the character in play, thus gregor cant resolve.

Very simple way to settle this:

If I trigger Gregor and you save the character, can I trigger "after a character is killed" Responses? No? Because the character is considered to have never been killed in the first place? Then the kill effect must not be considered successful, event though it was initiated completely.

(It is worth noting that when a cancel is used, you are not "canceling during initiation." Initiation is completed for canceled effects, just like it is completed for save effects. Otherwise, the cost would not have been completely paid and could be canceled, too.)