A little searching shows that there have been some failures of the oil pump gears on the 4.6. The complainees are generally of the "road racer" persuasion which should not apply to your vehicle.
They mention that the gears are powdered metal so I would say that it is possible anyway for the pump drive gears to fail.
Changing the pump is a major undertaking and to be honest, I would consider the timing chain/tensioner setup at the same time.
However, this chain/tensioner setup is expensive.
Since the story is still a bit sketchy to me, I can only add a couple of comments.
One is that if the oil pump is questionable, any problem is easily verified by connecting an external gauge and checking the oil pressure, if any.
The second point is this. If the engine lost oil pressure and was making noise my feeling is that there is crankshaft bearing damage to some degree.
This means that if you spend a small fortune on the repair the vehicle may start up, knock, and lose oil pressure especially when warmed up.
It's also possible that problems may not surface until later on - 6 months or a year down the road.
If the oil pump legitimately failed, and this were my vehicle, I would drop the oil pan and pull some rod and main bearing caps. This would give a general idea of how the bearing surface looks and if any underlayment is showing then I would not advise a new pump, chain, or anything else.
It would be decision time on a new engine.
JMHO anyway and good luck. Hope this works out.