I see all the Niner games and I don't think you could call me a blind homer.
If you're looking for a best guess, I would say that Barlow will be given more of the load in the beginning of the season as Gore gets back to full speed. I haven't pimped Gore as much as Otis on these boards, but he does look special when he's in the game. If both are healthy, I believe Gore would get the majority of the carries as the season goes on. Barlow would definitely still share some carries, regardless.
A decent strategy might be to grab Gore and Barlow with lower round picks, with the hope one of them would end up as a #2 back at some point. Most of the country thinks SF is a fantasy black hole, so both backs might drop in a redraft. Around here, Gore will probably be grabbed too early. I personally think you would get a serviceable to good 2nd back when one of them inevitably gets injured. Gore gets the injury-prone label, but Barlow hasn't shown he can play a full season- and he came into the league the same time as LT2 and McAllister. Also, I've seen signs that their o-line is starting to develop and you will see the beginnings of a strong ground game sometime next season.
Long-term prognosis: Nolan knew about Gore's shoulder issue which came up early in the season, but Gore still wanted to play, so he played. Nolan took it easy with the number of his carries, knowing Gore would have to have corrective surgery after the season. He's shown to have an outstanding work ethic and has proved his toughness. Long-term, unless Gore has Ronald Curry-type luck throughout his career, I think he will be the back of the future for the Niners. Nolan drafted Gore himself, has always had positive remarks about Gore & Barlow, but has been more effusive in his praise of Gore. Also, the Niners passed on a conventional rb in the draft. Michael Robinson is intriguing and we'll have to see him in pre-season action. He's already garnering a buzz starting from his rookie camp last weekend. Hicks is good in small doses and could be thought of as a poor (maybe destitude) man's Willie Parker.