Some people found shavings and broken plastic pieces,replaced just guides and chains,and had no further problems.
My guess is that engine's components are fed with oil passing the filter before,otherwise it makes no sense to me.
I am at the same situation right now...when I bought my X5 it had the same problem,but instead of just changing broken parts I was told to swap an engine...and here I am again after 60,000 kms and 4 years.
So,read more stories..have a look at these two links about VANOS seals for M62 engine.
Beisan Systems - Procedures - M62TU Vanos Procedure

Beisan Systems - Products

Noise issues.

Still have my '03 4.6is full Dinan minus SC. 158k and runs strong as hell and fast. blk/blk, every option, factory 20s new dunlaps, factory 19s new hankooks. It was to be traded in but we held off. I drive it daily. Just put an entire new cooling system in - couple hose leaks, figured do it all. VCG are leaking a bit - typical. It can be gone for $10k if I don't have to go thru the trouble of listing it. I have a factory dog divider too but rarely used. Not too keen on our cocker spaniel in the X but if you have to do it, the divider is a must.

Just replace the broken bits and enjoy that motor for another 100-200k miles. It really does deserve to be repaired an not replaced.

After bouncing around to a couple different shops and seeing estimates from $9600 to $15,000 we finally settled on Strictly BMW in Bellevue. I've had them do some diagnostic work for me on other vehicles in the past and enjoyed working with them. They really took the initiative on this and did a full assesment of the engine rather than just saying it needs to be replaced. Jeff at the front desk is knowledgeable, and great to communicate with. Was like talking to a mechanic, and not a salesman.

Long story short, the oil filter did it's job in preventing the major particles from getting into the engine. They dissasembled and cleaned the oil pump rather than replacing it saving me $2000 (their recommendation was not to replace it based on their findings). Timing chain sprockets were good, so after replacing all the guides, chain, various hoses and sensors since we were in there, the total came out to $4600. We're going to do another oil change after running through a tank of gas to analyze the oil, but so far so good. She runs like a champ!

Glad to hear you are back on the road. Us 4.6 owners need to stick together and share these stories.

I'm curious to know more about the days/months/moments leading up to the failure. I want to do everything I can to mitigate further damage. What's really scary is that it seems like the timing chain guide can fail with little warning.

Yep, there was almost no warning other than the whining sound the day before, which sounded like a failing power steering pump.

Strictly BMW said last year they've done like 3 or 4 of these jobs on the 4.4 engine. With the guides it seems to be an issue of age rather than mileage. I suspect this will be a more prevalent issue in the coming years.

I think it's pretty well prevalent already. It would be interesting to know the average age/mileage that these failures happen. I've seen failures at 100k, and one member mentioned his buddy's 740 made it to 325k on the original guides.

Previously, did you get any chain noise on start-up?

Strictly said mileage was all over the board, which is why they think age is the common factor. I would guess it's issue of engine hours more specifically. Too bad we can't track them like a diesel truck.

Literally a split second of rattle was noticeable on a cold startup, but that was it. I haven't really noticed any difference since the work has been done either.

I read it somewhere that the oil service indicator is sort of engine hours/mileage indicator,because its pace is triggered by many inputs,like oil temps ,revs ,miles traveled.Too bad it only assumes you are always using a genuine bmw oil,which has predictable properties which data in processed on.
I might be wrong.