Can the DAO vote to unlock all 230M AST if they choose to?
Can the DAO decide to unlock any amount of these tokens at any time?
Theoretically they could vote to do so (e.g. if someone does a 51% attack on the DAO). But the vote itself is a signal rather than a hard governance decision since voting is done off-chain. AirSwap itself is stewarded by ConsenSys, so there is an additional layer of checks in place.
If the DAO does not decide to unlock them, what happens after three years?
That would be a question for the future DAO to decide. The AirSwap core mission and vision will remain the same, to build high quality decentralized p2p trading protocols to support the ecosystem. The crypto space moves very fast, and its tough to project what the space might look like in 3 years time.