I think it's the older guys, of my vintage (b 1964), and may I assume, Rob, of yours, people who are old enough to remember buying from Squadron at their original bricks-and-mortar location, or via mail order up through the 90s, who will lament Squadron's demise the most, if it is indeed going out of business. They would be the longest-served customers, and they have a nostalgia for the days when Squadron was pretty much the only mail-order option, or the best-known.
For me, personally, I never dealt with them back then, because the small local hobby shops run by a sole proprietor were still common. I bought everything I needed there, and at the other stores that sold model kits and paints. I think I saw an ad for Squadron in "Boy's Life", when I was a Scout, but paid it no mind.
I never even bought from Squadron till we were into the Aughts. I still could buy supplies locally, and like Rob, as soon as I joined eBay, I bought almost all of my kits there. Since I build mostly old kits, this was the best source for me, along with buying kits at club meetings and model shows.
By that time, Squadron really was not much better, if at all, in its selection or service, than the online vendors who emerged, like Roll Models or Sprue Brothers. And I could buy things like paints direct from manufacturers. The catalogs only reinforced this in my mind. They had a lot, but you could find other things elsewhere, often cheaper, and often without the wait.
So I feel sorry for Squadron fans, for seeing an old friend go, if it is, and for the employees who will have to find new jobs. But at this point, as far as losing a source goes, I think many will just say, "Meh".