They should have taken Rhaegar captive

[Megorova]

On 6/3/2018 at 4:00 AM, Canon Claude said:

Maybe Rhaegar makes a deal that he goes to the Wall for his crimes then, and Viserys or Aegon gets crowned.

Then Viserys' regent would have been his mother Queen Rhaella, and Aegon's regent would have been his mother Princess Elia. And both of those women had a grudge against rebels, that, in case with Rhaella, killed/deposed her husband Aerys, and in case with Elia, sent her husband Rhaegar to The Wall. Both boys would have grown up hating Starks, Arryns, and Baratheons. Eventually they would have used first opportunity to get revenge for their fathers.

On 6/3/2018 at 3:42 AM, Canon Claude said:

Of course there’s a few issues with this setup, namely Robert and Lyanna. Robert would never forgive Rhaegar for the insult done to him, and he would never get over Lyanna’s abandonment of him (assuming that truth comes out).

Ned's father and brother were killed by Aerys. Jon Arryn's nephew and heir was killed during war. Cat loved Brandon, and lost him because of Targaryens. Lysa had to marry with a man old enough to be her grandfather, instead of marrying with her beloved Petyr. King Aerys took Elia and her children as hostages, even before Rhaegar went to Trident. So Starks, Arryns, Tullys and Martells, same as Baratheons, would have never accepted another Targaryen King. 5 Kingdoms out of 7 were set on removing Targaryens from Iron Throne. So Robert's death wouldn't have changed anything. Ned still wouldn't have wanted to become King, same as Jon Arryn. Thus if not Robert, then Stannis would have became next King of 7K after Aerys, and married with Cersei instead of Robert.

[theMADdestScientist_]

On 6/3/2018 at 3:52 AM, Valyrian Blade said:

He died in single combat, he didn't yield. Pretty much impossible to take him hostage. 

Pretty much this. Robert had to kill Rhaegar or be killed by him. There was no way Robert would have been capable of taking Rhaegar as a hostage.

Besides, Robert would have never let him live, as Robert wanted the throne that was supposed to be his.

[LindsayLohan]

Some high-quality fanfic going on here. 

Reality:  Rhaegar was a piece of shit who got what he deserved.  One of the few people in ASOIAF to meet an appropriate end (along with Ser Gregor, Ser Armory, and the Goat of Harrenhall).