If the sleep, he shall do well - Sleep was regarded by the Jews, in sickness, as a favorable symptom; hence it was said among them, “Sleep in sickness is a sign of recovery, because it shows that the violence of the disease has abated” (Lightfoot). This seems to have been the meaning of the disciples. They intimated that if he had this symptom, there was no need of his going into Judea to restore him.
Related Commentaries of John 11:12
John 11:12
12 Then said his disciples, Lord, if he sleep, he shall do well.