i don't breed them but I suppose that like for the others cockroaches, that is impossible to give a rate with certitude: The factors involved are too numerous. If you take 2 colonies of the same cockroch's nymph and the same number in 2 differents boxes, with the same parameters for both: you'll certainly not have the same number of cockroaches at the adult stade in the 2 boxes.
from a mathematical point of view. if you take one couple:
adult female - adult male
adult female - dead male
dead female - adult male
dead female - dead male
==> 1/4 = 25% of chance that the couple become adult.