I'm pretty sure that's not the slightest bit true. I have a couple of very good music stores here and I myself purchased the Op 599 set in paper volume only a couple of years ago. I'm sure there are Schirmer editions still printing it. Czerny isn't one that will fade out over history.
Have you seen this site as well??? https://imslp.org/wiki/Category:Czerny,_CarlWhile a lot of these are scanned from out of print books, you know that the ability to get it in a paper book is also still around. I think because of the younger generation using digital books and prints, that the music won't be lost to the ages... but will become harder to get in paper format. I think it will however live on the internet for a long, long, very long time.
The Italian musicologist Luca Chierici has been digitalising Czerny scores for the last 15 years at least.I think it is about 90% complete.His original works are beginning to be more widely recognised and the future looks good.