First, I'm not a Mercedes mechanic or a mechanic at all, really.

In my experience, when the can bus goes down, it's almost always one of a few things.

1) Broke/grounded wire. A broke or bad connection can be hard to diagnosis with a multimeter, you need to load the circuit. But if you're seen multiple faults, this is less likely.

2) A module on the can bus is bringing down the entire network. On a crank/no start where there's no CAN activity or faulty activity (i.e. low amplitude or the wave forms don't match) I've had a lot of success unplugging modules and seeing if the network comes back. I've seen many an ABS module take down a CAN network causing a no start. You pull the connector and brake fluid starts pouring out.

3) ECU. It happens.

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1997 E300 Diesel - 222K miles