It IS a judgment call.
Most often, a moose properly hit goes down within a few seconds.
However, If he decides to bolt for cover, then additional shots may be in order.
Most of the substantial number of moose I have shot were dead within 15 yards of the spot they were shot.
Probably a half dozen tried to make tracks, but, being prepared for that option, an extra shot or two reined them in.
One cow moose, shot just a bit far back initially, soaked up 4 shots before she hit the ground some 150 yards away from where she was at first.
This helps one appreciate how important that first shot can be.
I deplore shots in the hind quarters of any game animal, and try to avoid them.
There may be times when the difference between a lost animal or a long tracking job and a quick dispatch involves a shot in the rear end.
This is justifiable, IMHO.
I once shot an Elk which was running straight away after it had been hit in the neck by another hunter.
The neck shot dropped him right there, but he bounced right back up and headed out, fast.
I was packing a 7mm STW, driving a 160 Partition at 3200 or so.
I aimed for the center of his rump and touched one off [shot was about 140 yards]
Missed the center by about 1", broke his pelvis, but besides a bit of a stumble he continued on.
He was out of sight over a small rise before I could shoot again.
But, he had collapsed within about 65 yards of the shot, and only needed a finisher to complete the operation.
I recovered that partition in the front right quarter.
What really was surprising, the bullet had not hit the gut and opened it up.
It went through the top of a lung, and did substantial damage to it.
To my way of thinking, I did the right thing. He never made it to the bush, and not a lot of meat was lost.
If he had not been hit already, I would probably have passed on that shot.
Regards, Eagleye.