So I'm in a bit of a hurry, going away for a long weekend, but will try answer your questions.
How Far were they from the group?
A fair distance away, like I said in a later post, it was the end of the session and we were wrapping up so I did a montage of the ranger tracking and killing the surviving orcs leading into a scene setup for the final encounter with the Orog. At all times I asked the PC if he desired to pursue the orcs to their ultimate death including their leader. He confirmed the character would do so, given his racial hatred for orcs (tied in with the class).
As for the chase mechanics (30 feet) and possible exhaustion, I hand waived all that given RL time pressure, so I just mentioned that the orog would be keeping pace. Furthermore I did not have the orog attempt a ranged attack - that would have perhaps resulted in either capture, but more than likely death. Having the elf captive would seem unnecessary effort by the orog, and to be honest I've already done the captive-thing to another of the same player's characters in a concurrent campaign.
If he were tracking them and caught up to them, how long did it take. If he went a sizeable distance from the group to the point that it was over an hour away or some crazy stunt like that I probably would have no problem having the Orog feel safe. Having him chase down and slay the Ranger after the Ranger got tired (if the Ranger got tired before the Orog which is feasible) if it is that far is just part of the game.
Anything from 20 minutes away to an hour seems like what I had in mind, but keep in mind this is 20-60 minutes away from the owlbear encounter not from the encampment. So no it was not that close.
Why would the Orog pursue after having their entire group wiped out. If the Orog was insane the Orog should have remained to battle the group instead of fleeing in the first place.
Different circumstances.
Some of the orcs were preoccupied with trying to maintain the owlbear in the net and all of them were surprised by the attack on them by unknown assailants from the foliage. When most dropped to spells and missile fire, the smart option was for the leader was to flee. Facing an elf on his own, without the element of surprise, is a completely different encounter altogether.
He tried to flee but he was tracked down by the ranger. This time though the ranger was not able to capitalise with the stealth. Hence the cinematic face-off.
Hope I managed to cover everything.