That is just one example, no doubt that are plenty more businesses that have established a high volumn of cross border trade over the years of peace. This entire mess could well boil down to which side is most willing to suppliment the loss of income attached to brexit ...... is Boris willing to throw millions into NI in order to avoid disaster ? same applies to the EU.
All of this is nothing compared to the possibility of a return to 'the troubles' as they were called. Whilst the majority certainly dont want that, there is always a minority on both sides that will happily start rising up and challenging authority.