Do they simply return to the Force pool so they can be built again? This scenario results in overflowding of Soviet Guard troops in the map, where they make a majority of forces.
The Soviet 4-4 Guards Infantry Corps is a very "in demand" unit.
It is good on the map because it makes a Soviet BG when it dies.
It is good on the map because it can be fed 1 Soviet PP to make a 7-4 Guards Infantry Army (reduced).
It is good in the Force Pool because it is what you want your Guards Infantry Armies to break down into should they be reduced.
But there are only 5 of them. (6 if you're lucky.) Like many other unit types in your force pool and change box, these units must be "managed."