Send them in and cheerfully pay for the realignment. Packed in your luggage, the radical, rapid, changes in both pressure and temperature, coupled with a few hours of constant high frequency vibration, is more than many binoculars were designed to, or can reasonably be expected to, withstand. Even packed as carry on, the vibration is not good for any optics. Its a fact. If you fly with your binoculars, expect them to go out of alignment more often than other units of the same make and model.
Scopes are harder to check for alignment, but they too can have problems.
I know of no easy, reliable test for optical alignment in a scope. Step 1 Take a fairly new, clean, unfaded dollar bill. Move the bill back in until they separate again. Do this several times until you are confident that you can see the point at which the lines first separate. Roughly measure the distance from your eyes to the bill.