I also wanted to do something similar with my Hawke. He was always a kind, diplomatic Hawke but he felt really guilty about everything that happened with Anders, who was his LI, and Corypheus so he felt it was about time he made up for it and sacrifice himself. Then Hawke goes "Say goodbye to Varric for me" and I get back to Skyhold and Varric goes "Where is Hawke?
" and I just couldn't do it and had to reload. Oh well, Hawke, I guess it is back to Anders-babysitting duty for you...
What I think is interesting about that choice between Hawke and the Warden (Alistair in my case, argh, the things I did to save you and my PC in Origins) is technically the one you left behind in the Fade could still be alive and for all we know, worse things happen to the one who goes to Weisshaupt, with what is going on down there. I hope not, but that would be quite the drama.