Hi; I just found a new Coldhands spoiler:

Response: After you play Coldhands from your hand, choose 1 non-Army character controlled by each player, if able, and remove those characters from the game. When Condhands leaves play, return the removed cards to play under their owners' control.

So this removal from game cannot be saved with duplicate as I see as duplicate is not valid against "removal from game"

Saving with duplicate

If one of your unique cards is about to be killed,
discarded from play, or returned to your hand
or deck, as a triggered “Response:” effect (see
later), you may discard an attached duplicate to
save the unique card from being killed, discarded,
or returned to your hand or deck.

Another question on this: I choose my Coldhands which i just marshalled, which means it will leave game and then placed back. The only change in the field will be that one character from the other player(s) will loose every attachment, duplicate and power on them, right?

Duplicates are now a save from any "leaves play" effects. It is in the FAQ.

I heard that he can be used as a "blink" effect like you describe, yes. However I am hoping that when the time comes we will have more clarity. We are 4 months out from that chapter pack sadly.

From the FAQ:

(4.2) Duplicates
The text from page 19 of the Rulebook should read: “If one of your unique cards is about to leave play, as a triggered ‘ Response: ’ effect, you may discard an attached duplicate to save the unique card from leaving play. This includes, but is not limited to, an effect that kills, discards, returns the card to hand, deck, shadows, or removes the card from the game.”

Duplicates are totally allowed.

Another question on this: I choose my Coldhands which i just marshalled, which means it will leave game and then placed back. The only change in the field will be that one character from the other player(s) will loose every attachment, duplicate and power on them, right?

If there was a duplicate on the target char, then the dupe would be used as a save and the power and attachments would stay.

Thanks for the answers.