I can't tell the extent of damage from that one photo, but if the crack doesn't go into the sapwood back, it could be repaired like Del mentions.
I personally wouldn't bother trying to repair it, even for a good friend, and even if I was confident of a reasonable chance of success. It's a thankless job, which is tricky, a lot of work, all risk with no reward to you. Ruddy, you make really nice bows, tell him he's better off commissioning a new bow from you that doesn't have any issues, for a price you are happy with.
It would be interesting to know how long the owner had this bow, and was shooting it for? What style of stringing the bow did he use(I'm guessing step through)?