Considering he's been their best player and will only be sidelined due to an injury sustained whilst playing for them, I think they'll extend his contract for another year. Would be incredibly harsh and insensitive if they didn't, he was one of their marquee incomings and would send the wrong message for potential signings.
Can't see any way they keep him, unless they're contractually obligated to - IIRC it was initally reported that certain metrics would trigger an automatic extension.
Since then though, all the reports were that Ibrahimovic was playing hardball over the deal - trying to secure himself a guaranteed 2 year contract, rather than the 1 year on the table.
If that was the case, and it's been reported that way in The Times and Telegraph, among others...then he just gambled and lost.