Na, you need to think the other way around. Usually, if a licensing issue arises, that means the person who gave GOG the permission to sell the game either no longer has the permission or never had it. That means GOG is potentially selling the game illegally. That is why most companies take it down as soon as they sniff legal trouble.

Problems with this can amount to (but not limited to)

- Shelving over all profits made by the sales from the moment they knew it was legally challenged to the new license holder. (Usually the claim would go against the current license holder, who recives a cut from GOG. But they can also make demands against GOG for their share). Courts could even go as far an see this as an "harmful exploitation" of said license, as GOG cuts into a potential buyers market for the next "licensed reseller" and hurt the original license holders business position.

- Removing the game from the customers who bought it during the "time of knowledge". As you cannot obtain licenses "on good believe" like physical goods, every license now sold could be void. Therefore GOG would actually need to remove it from the catalogue.

While it has been established by courts (German law) that removing the "middle man" from an legal chain should not retroactively affect the end users. This is based on the "protective worthiness" of the said end user. With this announcement the end user is losing quite some "protective worthiness".

Remember, IT law is still to a huge degree based on court decisions as the law doesn't keep up. And this behaviour isn't really something judges like.

Edit:

Oh, if the license simply "runs out" and a new deal can't be made, this all is irrelevant. What I typed only goes for a contested license. Which should be fairly rare in the first place.