I'll be very interested to hear Benzmac's response to this. Before my 240D engine rattled and died at 516K miles, it was still pegging the guage on the highway.
Since it isn't using a lot of oil and is not going dangerously low at idle, it may not hurt anything, but I expect that Benzmac will shed some of his experience and wisdom on this.
BTW, I bought a ragged 240D with a decent engine, swapped the engine into my trusty old 240D, and I'm back driving it 190 miles a day. They can't be permanently killed by anything less than 18 Wheeler. If it's ever killed that way, I won't have to worry about it.
'84 Euro 240D, 516K miles
'88 300E 5 Speed
Over 800,000 miles in