So sorry to hear that, what a bummer.
The good news is that at least it happened at low engine speed. So I think you can expect that it will not be too bad to repair.
I had a timing belt failure about 5 years ago in my 740 (belt that had relatively few miles on it but was OLD). It happened around idle speed and it broke the cam into three pieces! So I know how you feel.
But the good news is, on my car, there was no damage whatsoever to the bottom half of the engine. Pistons, rods, etc, were all fine. I replaced the cylinder head with a good used spare I had, and the car was back on the road the same weekend. So don't despair too much........ It happens.
The fact that the camshaft tends to break when timing slips on the D24 engine is actually a good thing in many ways, when you think about it. It turns the camshaft into a kind of sacrificial part, a safety valve that gets destroyed but saves other parts of the engine from more serious harm. You would rather be dealing with a broken camshaft than have to worry about bent rods, broken pistons, bent crankshaft, etc. Fortunately the cam breaks so fast that those other parts tend to not suffer.
All that said, I think the safest point of view is to figure the entire cylinder head needs to be checked out. I would not want to just replace the camshaft if it were me. I would assume any part in the head that took impact force should be considered compromised and replaced. That means all the valves and guides, all the lifters, and of course the camshaft itself. Probably also should get the cylinder head aluminum main casting carefully looked at by a machine shop. It is rare but not unheard of for the cam bearing towers to get physically damaged or torn off when the cam breaks so you want to be sure there are no signs of that or other harm.
The reason for this concern is that if you leave impact-affected parts in the engine that "look fine" but have unseen damage, you might get it running and on the road and seeming healthy, but then something could fail later on during operation that could cause much more severe harm. The common story of this is with a damaged valve that later drops its head into the engine and wreaks havoc. That is why you want to get all of those parts that could fail in this way after impact out of the engine.
Yet still, the good news is that with the D24 (due to shared parts with the extremely common 4cyl VW diesel), items such as valves, guides, and lifters are easily purchased and cheap. So the whole exercise shouldn't be too costly or difficult.
Goes without saying you should also do a careful inspection of the front of the crankshaft and the timing gear, and replace anything that suffered damage there. Probably at least the timing gear will need to be replaced assuming its "key" got torn off. Hopefully the nose of the crank is not damaged, although even if it does have more wallow in it you should still be able to use it no problem. Probably want to look at that before making any other decisions though.
Good luck and keep spirits up, it won't be too difficult to get it back to where you had it before, and who knows, maybe you'll get some more new parts out of the deal.
