I wondered how long their marriage would have lasted, considering his obsessive love of her. At some point, most sensible women will put the brakes on and say "No!"
On the other hand,if Snape had felt more secure in her love, might he have relaxed a lot and begun to act more normally with her?
Then I got to wondering how, in this AU, Voldemort would have died. One scenario I came up with was that Lily still dies, but Snape survives an attack on himself and has to raise his child alone. Would he have ever gotten past blaming their child for her death? Could Dumbledore have ever convinced him to protect his own child, the way he convinced Snape to protect Harry? And what would the poor kid's life have been like? (I shudder to think.)
It would be a neat thing to write. I'd prefer to do the version with Lily surviving, simply because I find the idea of writing about a marriage deeply worthwhile, seeing how the couple solves problems, and so forth. That is one reason why I wanted to write Narcissa Malfoy in a post-Hallows RPG I joined--because I wanted to explore her and Lucius' marriage. It seemed so much more deeply layered than I had expected, during that scene in Chapter 1 of Deathly Hallows. I was amazed at how subtly Rowling was able to convey deep trust--just by Narcissa touching Lucius on the arm. She never had to say a word to let him know she would think no less of him as a man if he surrendered his wand to Voldemort. I thought that tiny gesture was exquisite.
Maybe others got something else out of that scene, but that's what I got.