So I am currently re-watching the entirety of the the series and something that I have noticed is that there a quite a number of characters that die in the same fashion to the last person they killed on-screen.

Bellow are just some of the examples that I can think of right now.

Ned Stark - He beheads a deserter in the first episode and I believe that this is the last person he kills on-screen. I know that he kills Lady out of mercy after that, but we're mostly counting human characters. He is later beheaded himself.

Catelyn Stark - Cuts the throat of one of Frey's daughters before having hers cut seconds later.

Roose Bolton - Last person he kills on-screen is Robb Stark by stabbing him in the chest, and is later stabbed in the chest himself by his son Ramsey.

I'm sure that there are plenty others, and I would really like to know them so let me know if you can think of any more.

This is quite uclear to me. What he was thinking? This could have no good outcome of any kind that i can think of.

Why simply he didn't just let her marry Robert? Then after succeeding his father he appointed Robert as advisor or hand of the king so Lyana was close to him and they could have a long lasting lover relationship. As Robert was such a dick he probably didn't really notice or care just like with Sersei and Jamie.

But abducting her? How that could have worked in any way to even a moderately good outcome?