Believe the idea is to use them as territorial guards to free up more Russians for the front. In addition, I read that half the artillery shells fired this year were of DPRK origin proving that Russia is becoming very reliant on other countries equipment/resources to continue the war.
The idea that Putin will benefit from a long war may be another of his bluffs that has become gospel in the West as they're equally running out of men and materiel. That being said, still suspect they'll edge to the Donbas border, claim it as a victory and cause a cessation to this hideous war of conquest allowing both sides to claim "victory".