Every part of DOMA is essential to make it protect what it was intended to: marriage. Only one part falling will collapse the rest of it.
If Part 3, the federal recognition clause, is struck down, then counterfeit marriage will be exportable into every state. Technically, states which have their own marriage amendments don't have to recognize them for state purposes, but with the federal strings attached to all that a state does, how long will that last?
Only potentially exportable.
There are 40 states holding the line on traditional marriage. I don't think that will change a whole lot.