If anything, the fact this happened will have a positive impact on sales. First of all it's publicity. Second of all, everyone loves a victim. Third of all, it creates a fake shortage...therefore a fake urgency to buy later when it hits. WINNING!
For some of the smaller labels involved --- esp. those who are more catalog focused --- the fire was a pretty big deal. Imprints that had inventory of various titles in the 10-200 pieces range now have to contemplate remanufacture w/ minimum quantities of 500 and/or allow those titles to go out of print. This is not the easiest thing in the world to explain to an insurance company (i'm not saying it can't be done, but it's not exactly a snap-yr-fingers, here's a huge check scenario, either)
(the comments about dead/immoveable stock are right on...however in many cases the true wastes-of-space were already returned to the labels' own warehouses/offices/bedrooms. Shelf space at PIAS was at a premium, or so they claimed, and if you intended to keep thousands of records there that no one was ordering, they happily invoiced labels for the privilege).
I'm not so certain the publicity is gonna result in a windfall for anyone. Over there, anyway, there's probably a greater outpouring of sympathy for small biz owners other than the people who release Adele & Arctic Monkeys records (which sort of makes sense). Again, there's MUCH smaller labels that go through PIAS, but if they struggled to get on the public's radar pre-inferno, it won't be easy to do so afterwards --- especially if they're unable to ship physical stock for weeks or months.
The media appeal to purchase downloads from the labels affected is a nice idea but ignores the fact the UK's remaining independent shops might still be sitting on some of those titles...and this is exactly a moment in time where they're gonna need help, too (i have a sneaking suspicion the number of people hitting record shops in England this week might be even less than usual).