Which of the following would get me in the least trouble if I got stuck
in the station due to this (and my paper ticket not working)...

b) Pushing the emergency open button

I'd go for this one, and have done on several occasions.
The louder the noise it makes, the better. You'll also find that
several people will follow you through when opened, and any
RPI who turns up is going to have to contend with lots of people
rather than just one.

Of course, if you haven't got a ticket then, when you do get through,
you must at least attempt to seek-out a persun who will accept your
payment.

Richard [in PE12]