There is no way it would not have sold, especially as a kickstarter. The license pretty much prints money and there are lots of recent examples where people clearly buy the minis only.
A candyland themed reskin with a snake mini would have sold like hotcakes.
It probably would have sold, but 'like hotcakes' is not guaranteed.
To give some sort of comparison, Resident Evil 2: The Board Game, pulled in just under £1mil on Kickstarter, and last time I was in a FLGS, copies of it were on sale for 25% off, so not exactly flying off the shelves.
Resident Evil 3: The Board game, did similar KS numbers (its not on shop shelves yet).
Horizon Zero Dawn: The Boardgame made £1.3mil and has been 'a shitshow' with parts still not delivered to backers.
No idea how much Steamforged Games paid for the licences, but £1mil(ish) to cover IP right, years of development, design, manufacturing, shipping and distribution probably isn't printing money in the way that you think.
Also, the thing about buying a game 'Just for the minis' is that, if the minis are no good for a D&D/Pathfinder game (Yes, other TTRPG's exist but they have nowhere near the same support or following), then what other use are they?
(I guess Batman is such a colossal IP that it gets to be an outlier)
So in the case of this MGS game, they kinda had to get the game right as well, because it absolutely would have hit tables, and if it was a bad game, it would be discovered very quickly, and while they'd always have the money from KS backers, FLGS sales would probably dry up very quickly, and they need those sales to make the game worthwhile as a profitable endeavour.
FAKE EDIT: I just remembered that IDW themselves have a few Kickstarters for licenced games behind them - TMNT, Nickelodeon, Legend of Korra and Batman.
The only project to crack the £1mil funding mark was....... yup, it was the Batman game!
People just really like Batman don't they?