This is actually going to be easy to reverse. Just like in California, it will be easy to get a huge majority of voters to agree to change the State Constitution to ban homosexual ‘marriage’. This won’t even last a month.
Nope, getting a constitutional amendment on the ballot in CA is far easier than getting one passed in Iowa. It will be quite a few years before one can possibly be adopted, and there are reasons to believe that it just won't happen.
We have thirty states with anti-gay marriage provisions in their constitutions. As for the remaining twenty, they just haven't gotten around to legalizing gay marriage yet, but their supreme courts are taking them down that path. We might even see it happen by a legislature and an executive that is not willing to veto. That almost happened in Vermont, and if they get a Dem in as governor, it most assuredly will happen.