Of the two issues put forward (collateral damage risk; shooting at the back of a felon who is no longer shooting) only one would apply in my neck of the woods, and that would be the collateral damage.
As far as shooting in the back, or shooting at a fleeing felon, or for that matter continuing pursuit of a fleeing felon:
The guy was wanted for drive-by shootings, and had just fired on police. By law and by local department policies, those factors made the felon a lawful target until he surrendered. He didn't have to approach, he didn't have to continue to fire, all he had to do was fail to comply, and shooting him was lawful and in accordance with the policies I've read posted in local media.
Collateral damage could have been a legitimate reason to consider ceasing fire. I'd have preferred to see fewer rounds fired in a residential neighborhood.
But that has nothing to do with whether the guy was no longer shooting at, nor facing, the officers.
He only sowed what he very actively had reaped.