Situation as follows:

I've got Hoster Tully (Conquest and Defiance-Version) in play and Banner for the North attached. I somehow manage to give him an military icon and use him to succesfully defend an military challenge but my opponent has an participating character with deadly and i have none.

1) Am i able to reattach Banner for the north to an other character before Hoster Tully dies?

2) If it is possible and i do so, does he lose stalwart?

3) If Hoster Tully keeps his stalwart can i draw himself with his response?

I am quite sure 2) is a yes and 3) a no but i would be happy about confirmation. Thanks

1) You are not able to move the attachment around anymore once you have attached it to a character. It becomes an attachment with the text in the quotation marks and loses the rest of its text, so you are not able to move it around from character to character.

As such:

2) He doesn't lose the Stalwart keyword (but if you could move the attachment, he would lose the keyword because there is no moribund state for an attachment being moved from one character to another - and this would mean he dies for real because Stalwart acts as a replacement effect when the moribund character actually leaves play)

3) You will never be able to draw a Stalwart character in the response window to that character being killed (Kyle Condon is another example that prompts this question quite frequently), as the character is still on the board and moribund until after all passives and responses are complete. In other words, Hoster is (and inherently must be) on the board when you use the response, meaning he is not one of the 5 cards on top of your deck when you do so.

1) You are not able to move the attachment around anymore once you have attached it to a character. It becomes an attachment with the text in the quotation marks and loses the rest of its text, so you are not able to move it around from character to character.

This is not actually true. There is nothing in the rules that says cards like this lose their printed text (and only have the gained text) when they becomes an attachment. The Banners keep their printed text and can be moved from character to character when the regular Response conditions are met. NOTE: this is not the case for events-turned-attachments (like He Calls It Thinking or Risen from the Sea) because the FAQ specifically says that events-turned-attachments cannot trigger their event text again because event text is assumed to be usable only from hand (unless specifically said otherwise).

That said, the answer to #1 is STILL "no" because Hoster will die for Deadly (or claim) and his attachments passively discarded before you get to the Response step for the challenge. The attachment will already be "moribund:discard," so even if you move it to another character, it will still be discarded at the end of the window.

Thanks, Ktom, it was the events-turned-attachments precedent that I had in mind when answering the first question, so my mistake on that front

Thanks so far! But that answers lead me to another question: Same situation but now not hoster tully has Banner for the north attached but another character in play. Can i attach Banner for the north to Hoster Tully to give him stalwart before he dies?

No. You run into the same problem of timing. It looks like this:

1. Determine winner/loser of challenge. <-- Hoster wins the challenge here for your OP scenario

2. Resolve claim. <-- Nothing happens here because you won on defense.

3. Award unopposed. <-- Nothing happens here because you won on defense.

4. Award Renown. <-- Nothing happens here because Hoster doesn't have renown.

5. Resolve Deadly. <-- This is where Hoster dies because you lost the Deadly count.

6. Passives to 1-5 <-- This is where all the attachments on Hoster would be discarded/go moribund.

7. Responses to 1-6. <-- And now HERE is where you can finally trigger Banner for the North, too late to help Hoster (he's already "moribund:dead pile" from #5; too late for Stalwart to change anything).

8. End window.

now it's clear. thanks!