My reply to @T-K-G from the show thread showing how I would have kept Oberyn alive:
Tyrion's storyline could be slightly changed to his being exonerated through Oberyn winning the trial by combat but knowing that Cersei will have him killed anyway, Jamie and Varys set it up for Tyrion to secretly get out of King's landing without Cersei finding out. The rest of Tyrion's story can play out exactly like in the books from Jaime confessing about Tyrion's first wife not being a whore and that Tywin forced Jamie to lie to Tyrion which leads to Tyrion turning on Jaime to him then finding Shae fukking Tywin and killing his father in a rage thus becoming a wanted man again.
Oberyn could have been shown to have sustained some injuries in the fight with the Mountain that precluded him from killing Tywin himself. Oberyn's character could then become a merged character with his brother from the books. Say Doran dies of some illness and Oberyn becomes the new ruler of Dorne which then makes him have to leave the Small Council and King's Landing in a hurry before he can kill Tywin himself...with season 5 featuring a bumped up presence of Dorne in the show then it becomes very easy to just have all of Prince Doran's storyline from the books be carried out by Oberyn with the excuse for Oberyn not going after the Lannister's himself being because he has accepted the responsibility of the ruler of Dorne and his temper needs to be controlled. So then Oberyn becomes the one plotting against the Lannisters and wanting to align with Dany so she can claim the Iron Throne.
i feel where u coming from because a few weeks ago i said i wish they would have combined doran and oberyn too, but that was just my love for the character talking. it really wouldnt work because if oberyn doesnt die, there is no need for tyrion to escape. if oberyn doesnt die, there is no reason to believe that oberyn and tyrion dont just walk out of kings landing together and head down to dorne peacefully since tywin or cersei really have no legal way of killing either of them without setting off a war, especially since tyrion would be under oberyn's protection.
also, you cant just suddenly decide that doran dies from some random illness. if they WERE going to merge the characters, they would have had to start from the beginning and not even mention doran. then if u have oberyn as the prince of dorne, that changes the dynamics of the sand snakes and arianne wanting to wage war, while the prince of dorne preaches patience because he has a secret pact with the targaryens. if oberyn is in doran's place, and he knows about the pact, why behave so impatiently at kings landing? why not just wait it out? its just too many strings to tie up if u leave oberyn alive at this point. im sure they COULD have thought of ways to do it, but too many other things would have changed. im not one of those book readers that feels everything HAS to be exactly the same, but too much change isnt good with this story since its all connected.