If it's a conscience vote, as it should have been, you can abstain. Clare, like the rest can vote however the frick he wants. The plebiscite, as reiterated a bazillion times during the whole shit show, isn't binding. It comes down to how safe he feels his seat is, to whether he's confident enough to go against his electorate.
Abbott, is a whole other kettle of flyblown fish. As the driving factor behind, and poster boy for the plebiscite, he should be required to vote with both his electorate and the national result, or be sent an invoice for the cost of the whole thing.