So what do you do?
Stephen over on Software advice has a blog post wondering this very question. He has a survey running to see what people do. Now this is aimed at the US market more than European but there is no reason it does not apply in Europe either.
The survey and blog post are here. It is only one question not one of them 20 minute marketing surveys.
Personally if my favorite craft beer is not available, I pick something else and it may not be anything like what I wanted in the first place. Sometimes I just want a Galway Hooker only to find out it's all gone. I often crave Hooker because it is not available in bottles so I can only get it on tap. If they have none then I can always order another IPA of some kind, although I was treated to a complete IPA shortage at The Bull and Castle once. Not a drop or bottle to be had in the whole place.
I certainly never go to another bar, unless I am going to one of those pubs that only serves one craft beer and when I find out there is none at all, then I will walk away.
I remember going to The County bar in Lucan because they have Hoooker and O'Hara's on tap. Hooker was all gone so I had O'Hara's stout on tap which is not as good as from the bottle.