MB says the "wear limit" is below a quart per 200 miles. I interprete this to mean that the motor is so wore out at this point that it won't start any more.
In practice motors with more than a quart per 1000 miles usage are experiencing some form of failure.
On the older 615/616/617 engines the cars would quit starting during a North Florida winter when they got below a quart every 3-500 miles.
Unlike gas motors the diesel doesn't really mind burning oil. (It will cause carbon problems at times). As long as you have compression and can keep up with the oil, it doesn't matter except as an indicator of age.
Owner 24 bay BSC
Bosch Master, ASE master L1
26 years MB technician