Unless you KNOW that something let go, there's a really good chance that your oil pressure relief is just stuck, or the o-ring on the oil pickup is hard and sucking air.
I just replaced the pump in a 2009 6.0l for the same reason. Really low oil pressure at idle, and still under 20psi if you rev it up. A replacement Melling oil pump is $50 and comes with the O-ring. You don't HAVE to drop the pan to change it. I've done two now by only pulling the timing cover.
With higher miles, I put a high volume pump on the truck I just did, which was $100. A LOT cheaper than replacing the engine (or truck) when there's nothing wrong with it.
For a sanity check, do a used oil analysis. If it comes back clear, and no bearing material present, then you know it's just the oil pump relief or pickup o-ring. Much cheaper fix than a new engine.
My $0.02.
<edit> Oh, I forgot about the stupid screen under the oil pressure sensor. If that screen wasn't replaced or removed when the sensor was replaced, it could be clogged, which would look like low oil pressure, though the engine would actually have plenty. I suggest pulling it, tossing it into the trash, and re-installing the sensor. Can also be done w/o pulling the intake. Takes about 15 minutes.
