#1 My hopes are with you, I have not prayed in a long time, but will try for your son.
#2 This may sound corny, but I just watched the Halmark special (fictional but good) about a little girl who had cancer.
The family spead up the hollidays so she could have them all in what they thought would be a short time. (happy ending, she survived)
I know your son is old enough to know the odds, but for his little girl, the family, and himself, this might actually be a good idea. If she misses school, so what, time with dad is the most important thing right now.