As I am not too familliar with the duplicate mechanics I am a bit confused how Ser Davos would work with them.

Ser Davos: "Interrupt: When Ser Davos Seaworth is killed, return him to your hand instead of placing him in your dead pile."

So what happens when I have duplicates of Ser Davos in Play I can come up with two intapretations, one encouraging using duplicates of Ser Davos while the other actually would make you avoiding playing duplicates.

1. If You have Ser Davos with one or more duplicates in Play and he gots killed you get one duplicate back to your hand. As long he dosn't leave the board you could play that duplicate for free in your next marshalling phase, creatin a very hard to kill character.
2. Duplicates do not go back to your hand as Ser Davos is not killed (he is still on the board). If Ser Davos gets killed later (without anymore duplicates in play) you get him back on your hand, HOWEVER as there are copys of his card ion the dead pile you won't be able to marshall Ser Davos again, and he would end up as a dead card in your hand.

If you have a Ser Davos in play with duplicates, and he is killed you have two options.

1) Discard the duplicate to leave him in play.

2) Let him die and trigger his interrupt returning him to your hand and sending his duplicates to the discard pile.

The following is meant to help put that into perspective, but it might read as fairly technical and/or rules-lawyery. Feel free to ignore it and just go with JRosen9's description of the choices allowed by the rules:

It is important to note that a dupe (which saves a character that "would" leave play) and Davos' ability (which kicks in when a he will be killed/leave play) are not actually interrupting the same thing.

- Saves, like dupes, interrupt the initiation of an ability's effect that would make the card leave play (Step 6 of the "Process of Initiation" outlined on p. 10 of the RRG). They act kind of like a localized cancel, making it so that the effects of an ability are never applied to saved character in the first place.

- Davos's own ability interrupts the resolution of the ability's effects (Step 7 of the "Process of Initiation" outlined on p.10 of the RRG). You can't stop the fact that he's going to die; you just get to put him somewhere other than your dead pile.

So, if you take choice #1 of JRosen9's options, you discard the dupe in Step 6, stop the "kill" effect from being able to get rid of Davos in the first place, and actually cannot use Davos' own interrupt in Step 7 because his "is killed" triggering condition is no longer true. If, on the other hand, you take choice #2 of JRosen9's options, you are already past the point where you can stop Davos from being killed and leaving play. As such, everything in the "Leaves Play" section of the RRG (p. 12) is going to happen - including discarding power and dupes on the character, returning non-Terminal attachments to their owners' hands, etc. All you can do is trigger Davos' own ability here in Step 7 so that he isn't placed in the dead pile - which carries all sorts of bad ju-ju for unique characters.

one encouraging using duplicates of Ser Davos while the other actually would make you avoiding playing duplicates.

Choice #1 encourages the use of duplicates because Davos never leaves play, you keep him out of the dead pile, you don't have to pay for him all over again, and you get to keep all the power, etc. on him. There aren't a lot of situations where you're going to take Choice #2 instead of Choice #1 - just like there aren't a lot of situations where you're going to choose not to use a duplicate on any other unique character and let it die if you don't have to.

Choice #2 doesn't encourage or discourage the use of duplicates, really. It is just a consolation prize (keep him out of the dead pile and pay for him again if you have the gold) when you can't stop Davos from being killed.

Thanks for the clarifications. My main Problem was that I assumed that duplicates go to the dead pile insted to the discard pile.
So duplicates won't go back to your hand, only the last copy but as the duplicates go to the discard and not to the dead they are not preventing you from playing Ser Davos from your hand.
One last question. Lets say Ser Davos is in Play with a duplicate and gets kille by a "can not be saved" effect (for example "Wildfire Assault") I assume that the duplicate gets discarded while I get one copy back too the hand. However does that duplicate end up on the discard or the dead? As it is a "can not be saved" effect I cant use the duplicate to save him, so the duplicate would end dead pile preventing me from playing the copy I got back to my hand.

It would go to the discard. See "Leaves Play" on page 12 of the RRG.

Duplicates never go to the dead pile.

They either go to the discard pile when you use them, or they go to the discard pile when the original character leaves play (for any reason) and you cannot/do not save it.