I'll get the tough question out of the way, I do envision Robin's miscarriage to be a product of stress. Robin did not actually get pregnant until after Dallas left Shocker (or shortly before), so Dallas does not know Robin went through any of that. (I plan on D & R talking about it later, but as of right now, only Beau knows of the ordeal and only by accident.) Sterling's day-to-day abuse, the pain of losing Dallas, feeling isolated and estranged from herself did not foster a healthy Robin, no.
To answer your sweet, light-hearted question: Dallas would have reacted very positively! He was basically waiting for any reason to fall back in love with her, to see that the old her was still there somewhere, and that would have been the gesture to do it. He would still stand by his principals and such, and he would still be her friend for a while before anything more intimate, but it would have meant a lot to him. Sorry I'm cruel.