I'd be more concerned about ensuring Ovi still has effective playmakers and impact players on his line five years from now to ensure he has the puck in the offensive zone, rather than whether Ovi will be able to make an impact when he has the puck. He can score seemingly-impossible goals and his shot looks as good as ever, but he's not a guy who can produce offensively with AHL plugs by his side (in a way that, say, Crosby or McDavid can to some extent).
Backstrom's game has never been based on speed, which helps, but there's a good chance a year or two from now neither he nor Kuznetsov are playing anywhere close to 1Cs on the team, and that could impact Ovechkin's production. That, of course, would hurt Ovi's chances of catching up to the Great One.
Without Ovechkin this team would be a rebuilder. Every $ of cap space spent on players not-named Ovechkin is to give an Ovechkin-led team the best chance of winning a Cup, and Ovi of making history. If two years from now Ovi did look like an anchor and the team wasn't competitive, I don't think paying him $9.5 million would matter as the team would be spending far below the cap as a rebuilder anyway.
