I think that it's actually interesting to see the figures to put a bit of perspective into it. The Autoblog article says that Ford is the second best-selling car maker in Europe but, at least this year, it isn't. See page four of the attached PDF.
If we consider standalone brands then Ford is indeed the second best selling manufacturer, but I think this is short sighted and that groups should be considered as a whole. On that basis, even GME outsells Ford and Ford itself is placed fifth overall behind VW Group, PSA, Renault and GME. So perhaps if we only looked at sales figures they aren't that strong of a position, altough it isn't bad at all. Of the european heavyweights, only Fiat is behind in terms of sales figures.
Furthermore if they were to really exit the market their reputations would be probably heavily damaged making a future reentry very difficult and expensive for their respective parent companies. Let's not forget that despite the crisis and everything, Europe as a whole is still a pretty large market (3rd biggest in the world if I'm not mistaken).
However a very different story is unfolded if we look at the cars they make. Or, in other words, can GM and Ford really afford to lose all the engineering expertise derived from the R+D conducted in their European facilities? Both Buick and Chevrolet use Opel derived vehicles in both US and Chinese markets and Fords global Fiesta and Focus are basically European developped cars.
The good thing about the European market is that being one of the most demanding in the world it forces car makers to produce high quality cars which are sometimes easier to sell than cars from other parts of the world to Europe. However this can arguably also bring "desnaturalisation" of European GM and Ford products to Europe causing in reaction a less favourable opinion of the products in the original markets they were created for.
Another different question is the actual production process of these cars. Can this still be carried out in Europe? Possibly yes, but factories need to undergo adjustments to make the profitable again as they were sized for a market that no longer exists, and that maybe will never exist again in terms of volume. This aspect is probably the ones than needs the greatest changes and almost surely the ones that will be the most painful to Europeans.