Lots of fear mongering but I'm not sure I'm hearing a lot of facts.
First and foremost this law is about consumer protection. The idea that consumers can resell digital goods is, in itself, not necessarily a bad thing. After all, if you don't use a certain product anymore, why shouldn't you be able to sell it just because it wasn't delivered to you on a physical format?
How this would affect the games industry I'm not sure but up until this generation games were mostly sold on disk. Despite this the gaming industry has only been growing so it is probably fair to say the second hand market isn't exactly killing the industry. The same can be said for other similar industries. The music and movies industry are still alive and kicking despite second hand markets being available for over half a century.
As somebody else said, it is also a case of supply and demand. If everybody is waiting for second hand sales, the prices won't drop significantly. If the prices do drop quickly either a lot of people bought it at full price. Good for the dev/pub. Or it's not a very good game and people are dumping it. Bad for the dev/pub but not something the consumer can be blamed for.
It's also not like people will sell every game they have just because they can. I'm sure a lot of people like to hang on to their games, especially the good ones.
Of course there is also no reason to think reselling has to be free. Just as with reselling physical goods, in many cases there will be a third party involved that takes part of the cut. The platform holder could take a cut and share (part of that) with the dev/pub. Theoretically the fees could even be set up in such a manner that would discourage reselling. Though that would likely cause consumer backlash and probably further regulation in the future.
As for Indies in particular, if your business model is so cut troat that you are barely making money in the best case then maybe it's time to reconsider your priorities.
A lot of people so things out of a passion and barely make a living. That is an unfortunate reality we live in. Not a lot of people can so what they love and do it exactly the way they like it and live comfortably off it.
Being able to resell games might even lead to more people trying out games, which might be a particularly large benefit for Indies.
If any I think gaming is under threat more from lootbox crap etc. and the people that keep spending ridiculous amounts of money on that than gamers potentially being able to resell their games.