He may make it crystal clear that he's in total opposition to the referendum. He did veto this exact bill a year ago. If this referendum is less popular than he is (which I completely expect it to be), there's no way he'd embrace it--especially since he didn't the first time.
Even if he distances himself from it, there remains the possibility that the referendum will draw people (specifically young single women) to the polls who would not ordinarily turn out in a non-presidential year. Couple that with possible marijuana and gay marriage referendums bringing out young voters, Snyder would be in big trouble.
Not to mention the Unions who will coming to vote against Snyder in droves because of the RTW bill he signed that was forced through earlier this year. The Dems will hang this rape insurance around the neck of every Republican running no matter if they support it or don't. And what happens if Snyder comes out strongly against this something a lot Republicans probably support, he'll be seen as a RINO and they won't come and vote for him. In my view Snyder is toast this race is Lean D as I see it.
