He lost his court battle to force the local government running the dump to allow him to dig the last I heard. So I doubt it, he wasn't even allowed to really try.
Good chance those coins are 100% traceable. They were lost in the days before good privacy tools like mixers, and the database of the biggest exchange MtGox was fully leaked so everyone knows the real name, email, bank details, and date of birth of the owner of every old coin.
Very pleased I disposed of all mine long ago, and the Blockchain shows that so nobody tries to kidnap me for the keys.
I went back to the (french) articles making that claim in headlines and it turns out to be false, thanks.
He lost his appeal in his case against the city authority to search the landfill, so he can't ever search for it.
It's a bit buried in his feed in between the announcements about tokenizing part of these legally inaccessible coins.
I don't know where they get that 50/Ha figure. Paris is more dense than Seoul, with just over 200 people per Ha, or ~20k/km².
Figure would actually have been higher at the 1999 date of the cited source, too. The city is (slowly) losing people.