It's probably impossible to speculate with any certainty about what's going to happen. As someone in the UK who watches this stuff very closely, I would say that May's almost certainly not going to get her deal through, but there might be movement on a 2nd Ref or other compromise. Hopefully, this'll satisfy the "deep political change" that Macron's calling for and will allow for a longer extension - past June (and the Euro elections).
Otherwise, as things stand, it looks like we'll be out on the 29th, with all the chaos that that will bring. Game shipments won't be a priority, I'm afraid, so if there are huge backlogs at Dover and Calais (as has been predicted, and seems all too possible), the games are likely to be at the back of the queue.
"The pound will be very cheap..."
Always a silver lining! You could probably save 10%-20% of the price if you timed it right. Except... aren't the games priced in $? Which are then converted into £ or €? If so, the £ price should shoot up, compensating for the £ exchange rate plummeting. But the € price should remain about the same.