I can't imagine Valve won't find some loophole or way around this. Being able to resell digital games would destroy that economy. A possible outcome would be games in France are never on sale and they can only be traded within the French Steam economy. Can Valve still take a cut of all sales on their platform or add fees? Very curious how this turns out, but I feel like it's 50/50 whether this makes things better or…
Guess what the loophole's gonna be?
Steam will cost you 1 euro a month to maintain access, BUT WAIT, we've got this awesome "temporary introductory" deal where for every Euro you spend on anything in our store, anything at all, you get one free month of subscription! Yes, buy one brand new AAA game and you get 5 or 6 years of free subscription! Wowzers! What a stonking great deal for the consumer! Such an incredible deal that has been so successful that we're running it indefinitely, despite the fact it's totally temporary.
But if you do somehow manage to run out of months, you will indeed lose access. That part has to be real. And there will be a real "just buy subscription access" option, though nobody will ever use it because why just give Valve 12 Euro when you can buy a game with it instead?
I'm fairly confident in common law traditions, that would be too blatant and they couldn't literally do that. They'd sidle up in that direction, though, as close as they thought they could get. I don't know about how France's Civil Law tradition would take that, but, still, same principle; head in that direction as close as you think you can get. "As close as you can get" may in fact be quite far, but I think this is still the general direction you're going to see.