The best option would be if you could get a ride from someone at the conference, but as you mention a few drinks after
I’m not sure if there will be someone willing to drive.
Other options to get from the Maassilo to the Europoort P&O ferry terminal are quite limited. The only regular public transport that goes directly where you want to go is the bus you mention.
Other public transport is possible, but will take you 3.5 hours.
Credit:stackoverflow.com‘