That is possibly the most heart-breaking theory I have read and it makes me want to cry real tears. Good Lord, Ispan... 
On the other hand, that could also segue into an absolutely incredible (though highly unlikely) scenario where this happens: Solas turns down Inquisitor because of The Mission; Inquisitor goes on to sadly remain celibate (or maybe romances someone else, but it doesn't work out and they don't last); The World Is Saved, but as we all know, the game continues AFTER the main mission is resolved; so, after The Mission has been completed and if Inquisitor is currently (or has remained) single, Solas approaches him/her after all that time to initiate what had to be put off when The World Was Ending...
Solas: "Inquisitor... do you remember that question you asked me so long ago? Back when all this first started?"
Inquisitor: *hesitantly* "Yes..."
Solas: "The answer is 'yes'. In my heart, it was always 'yes'."

Bonus points for "premature fanjaculation". I died. 
Isn't it awful?
We need a yes or no now so I stop thinking up depressing scenarios 
"it was always 'yes'" *sniffle sniffle* It'd be sweet/sad if you could maintain a "what could've been" relationship with Solas throughout the game (would never happen but still fun to think about). The Inquisitor and Solas both know they wanted to be together but stay apart "for the greater good," meaningful looks and banter are exchanged, the Inquisitor absent-mindedly hums the Thedas equivalent of Katy Perry's Thinking of You. No sex required, just the two of them walking off into the sunset at the end of the game.
*curls up in a corner and sings under his breath* Don't worry about a thing,'cause every little thing gonna be all right....
Good choice, Bob got me through some awful stuff in the past so overcoming my Solas sadness should be a piece of cake for him! 