Known bug: When passing Derck, some players try to flee and run in the bar.
The door should have been disabled during battle, but isn't. This causes you to be stuck.
Hit A to attack if Derck is close enough, and W to follow him. If nothing helps, wait till Derck decides to stop looking for you.
Best to just knock is ass ass out when he attacks you. He deserves it.
This problem will be resolved next update.