A refund will not be possible, but don't worry, some weeks before the show you will be able to get tickets, especially for this third one which I suppose will not be completely sold out (as happened in Rotterdam lastyear which was the 3rd concert in Holland as well) So better first take care of you visa and get your ticket later. Presale MK is not necessary, I will buy my tickets from livenation.
Good luck and ask what you like! And keep in touch here, the weeks before the gigs we will plan a meeting early afternoon just near the venue. We have to queue not too late in the afternoon, so meeting will be around 12.00 or something like that.