They probably will bring in more over time, but North Korea has a population of only 26million and it is unlikely that Kim sends them all to die. Especially with South Korea having twice the population of North Korea.
But what will be fun, is Koreans being captured by Ukraine and South Korea buying them out.
Maybe they will, but I suspect this is some sort of PR stunt, probably to show a win for Putin. Maybe even to influence the US election, as Trump praises both Putin and Kim Jon Un.
Christianity is illegal in North Korea, owning or reading the bible is a capital offense. Yes you read that right, there is death penalty for participating in anything Christian.
Russia is a very Christian country, and there is not much chance those North Koreans won't be exposed to some Christianity.
This makes it doubtful these soldiers will ever be allowed back into North Korea. They are probably write offs in a political PR play.
The proxy Chinese may even deplete faster as they come already starved and don't have to be mistreated that much by their "superiors" before they can't run away from drones and other attacks.