Using another deadly weapon was out of question. After all, that scary bomb was enough price the enemy paid in this war to get rid of them.
As for sending another leader after Lingerie died, it was also out of the question. With the threat of the bomb, there was no way the enemy would throw another precious master like Lingerie here.
The instructions William left behind were all related to his plan to save everyone. He made sure to explain his plan to his friends, alongside instructions about how to aid him by laying down some preparations to save lots of time for him later on.
Then he kept walking outside, not bothered to follow the progress of war in this area anymore.
Once he got out of the portal zone, he returned to the underground city. The city was filled with tons of masters, waiting for their chance to join the war underground.
