Typically, diesel engines don't burn valves. I am ashamed to say, but I have run my high mileage 240D Jillions of miles without valve adjustment, although I would not advise that approach. I now have the wrench set which makes it much easier and I am more dilligent about this.
Predicting the mileage at which your auto trans will break is somewhere between difficult and impossible. The worst thing about an auto 240D is lack of performance. If the preventive maintenance has been performed on schedule, this is a low mileage 240D for this day and time. It will probably last many miles to come, but, of course, there are never guarantees.
If the trans currently looks properly maintained and operates well, proper maintenance will most likely keep it that way for many miles, it's not as if there's 300 horsepower to tear it up with.
'84 Euro 240D, 523K miles
'88 300E 5 Speed
'81 300D Daughter's Car
Over 800,000 miles in