I would have loved for the boys to have a stable and happy home even through I love the hunting storyline for Dean and Sam. And if Mary never ran into that nursery she might still be alive. But I think there are a few things that would have still happened, for example the demon blood problem, that would have came up sooner of later, obliviously. and there are a few story lines that still could have happened like the 'special' children being transported to an abandon town or Sam's death. And who knows if he would have came back depending on who knew about the crossroads deals. And OH MY GOD, The worst thing that would have happened is both the Winchesters boys would HATE EACH OTHER'S GUTS!!! It's sad to know they might never be happy. But at least they are saving people in the process.....

Tutorgirl95's answer pretty much sums it up perfectly

Maybe they'd have been OK for about 20 more years, assuming that neither demons, angels or random incidents still brought hunting back into their lives. But once Sam's demon blood activated, they'd be drawn into at least some supernatural events. In that scenario, would Mary realise that his visions/whatever other demonic power he could develop instead was due to her deal? And would that deal have even happened, without Dean's time travelling drawing Azazel's attention?