A better job opportunity shows up. Do you consider yourself and move on, or do you stick with your current company through the difficult times?

Depends, there are some companies that share the loyalty with its employees making them (the good ones) more stick with the company in good and bad, but there are companies that did not stand by the employees in the good days, you cannot except them to do the same in return. That in the difficult times, in normal times it depends on what as an employee you will gain with going forward? Personal gain, better pay, better experience, better position, or maybe all. It all goes down to the employee in the end and what s/he wants.

loyalty is a two way road of trusting, if you are being loyal to your company and giving them all you can and in return you are not getting what you deserve then the loyalty is missing from either of the side.