Personally I would evaluate more risk with the ferry for needlessly denied boarding (when your flight operates) than going to/from the airport. It was not shutdown by the last protest and don't think it will be again, just more difficult to access the airport due to the blockades. Worst case last tme was a 3km walk to get to the terminal -- not great but viable. Now the Airport Express has contingency plan to operate from Central only (bypassing the other stations), which should keep it running longer during protest times even if targeted. Also the airport has court order keeping out protestors from the airport boundary, not just the terminals, which may help keep the roads open.