I would doubt that it that plugging would hold. A crack like that generally creates a weak spot and will crack again.

Like tenpinitis said if it was bought from a reputable shop they should honor the warranty.

If not try the plugging. The only thing to lose is the cost of the plugging.

It can be fixed. For how long is the question. I have fixed a few and never had any problem with them. I have had problems with two ebonite balls that I fixed though, they cracked again.  Use a small drill bit 1/4 inch have worked for me, and drill into the crack as far down to the wieght block as possible, stop if you get to the wieght block, space the distance between the holes 3/8-1/2 inch apart. Start on the ends first to keep it from cracking more. In this case I would drill a hole on each end before the thumb and finger holes about a 3/8 inch away and plugg both holes @ the same time but only half the hole per day. I use plummers putty for the dam to keep the waste of plugg material down. You can reuse the plummers putty every time also. You want to go to the wieght block to help stabalize it again and to keep it from seperating again. This is some where to start if you want to save the ball.
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IN SEARCH OF THE PERFECT TWINS

if the ball has inserts they have just voided the warranty