I'm gonna be blunt here for a second- the people arguing that Kennedy would vote to maintain a state's SSM ban have no idea what they're talking about.
This sudden avalanche of gay marriage bans being overturned didn't come out of nowhere; it literally happened because that's exactly how Justice Kennedy engineered it in his majority opinion for Windsor.
As Ernest mentioned previously, Kennedy didn't use one of the more obvious or expected avenues of legal logic to reach that decision, but instead he went out of his way and circuitously based it on 5th Amendment Due Process grounds. I believe this was quite clearly intentional because it telegraphed to the Federal judiciary exactly how to overturn state bans on same sex marriage.
The 5th Amendment Due Process Clause is a restriction on the Federal government and it goes like this:
The cool thing here is that there's another Due Process Clause, in the 14th Amendment, that applies to the states:
The interpretations of these two clauses is identical and the only distinction of their jurisprudence is that the former applies to the Federal government while the latter applies to the states.
With Kennedy's precedent, it became extremely simple for a Federal judge to overturn a state-level ban. All that you have to do so is to replace "5th" with "14th" and "Federal" with "state", and you have an opinion that makes state bans unconstitutional, since the Constitution's two Due Process clauses are interpreted identically. Justice Scalia even called the majority out for setting it up this way in his dissent. It's why bans are now being overturned left and right even by conservative Republican appointees.
The majority in Windsor decided, with that opinion, that gay marriage was going to be legal nationwide. They probably felt such a ruling would be too broad or too unrelated to the immediate facts and circumstance of Windsor to do it in that case. They might have also hoped that the Circuit Courts would all take the hint and unanimously concur so that the Supreme Court wouldn't be forced into a controversial lighting-rod case where they directly legalized same-sex marriage nationwide in what would probably be a controversial 5-4 split mirroring Windsor. But regardless, a majority of the court established an obvious and intentional blueprint for nationwide marriage equality via the Windsor decision that we now see coming to fruition.
Kennedy and the four liberals who joined his opinion probably sought to keep the Supreme Court away from direct controversy- if de facto nationwide legalization occurs via Circuit unanimity then they may yet avoid the limelight entirely. Nevertheless, Kennedy's opinion set the groundwork and although the lower courts are now building on that foundation, if they aren't able to finish the job then Supreme Court will certainly step back in to explicitly mandate marriage equality. The Kennedy-led majority in Windsor knew what they were doing, and there's no chance any of them would back down rather than finish what they started.
tl;dr: No Kennedy won't vote to uphold state bans because literally the only reason they're all getting overturned now is due to an intentionally-crafted opinion he wrote that is literally making it all happen. Nationwide marriage equality has five guaranteed votes on the court
