Escape velocity
The escape velocity for a 25 km diameter asteroid (assuming it is spherical and the same density as the moon) is just slightly over 17 meters/sec (38mph). A lot of the blown off bits will have a velocity relative to the asteroid greater than this so will not be recaptured.
(The impact energy is equivalent to over 9000 megatons of TNT (!!!) so the broken off bits will not be moving at slow speeds.)
Biting the hand that feeds IT
