This is an impossible question to answer unless your crystal ball is well tuned.
The key is to wear out the hood hinges first. If you do this, then you are checking things often enough to keep little problems from turning into big problems.
There is no reason that it shouldn't make 250K, as long as it is properly cared for. There's no guarantee, but the closest you can get to the guarantee, is frequent oil changing and looking around alot every time you change the oil, to see what may be amiss.
The other ingredient is to feel and listen. If you do this, your car will almost always tell you ahead of time that some part of it needs attention.
Don't let it run down. If some little something is not right, fix it. If you don't, eventually, all the little annoyances will discourage you and you will want to get rid of it.
Best of luck,
'01 C Class, Six Speed
'84 Euro 240D, manual, 533K miles
'88 300E 5 Speed
'81 300D Daughter's Car
Over 800,000 miles in