There is only one offer that the Kohr-Ah make, which is:
Captain: Is there anything we can do to make you stop the killing?
Kohr-Ah: If you eliminate all non-Ur-Quan sentient races, including yourselves
then we will stop.
We have made this offer before. No one accepts.
So we cleanse.
It is strange that no one has accepted this. I would understand if they were asking for the race to commit suicide, which they still are... only later. Which would mean a race gets to live until all the other races are dead. Then these Battle Thralls would either commit suicide(unlikely) or be killed be the Kohr-Ah(who may be a bit angry that these races betrayed them).
This was probably an error in writing, they probably just meant suicide. Although such Battle Thralls still would be deemed insignificant by the Kohr-Ah:
Captain: Don't attack us! We are not your enemies!
Kohr-Ah: You are right.
You are not our enemy.
We have NO enemy
beyond the Kzer-Za, our partners in the eternal conflict.
You are simply... a spore, a seed.
Today you are nothing... insignificant.
But if allowed to bloom and grow someday...
someday, you might represent a threat to our freedom and security.
So we cleanse.