I've owned two Mercedes. The first one I had for 18 years and the only time it was ever to a dealer was to have the transmission serviced and to have the fuel injectors replaced. All the other work I did myself including all maintenance work.
My current car is a 1991 300E. I take it to a dealer to have the transmission serviced and I recently had to have the head gasket replaced. Other than that, I've done all the maintenance work.
If something should happen to me, my wife would be in the same situation you are in and would have to rely on someone else to maintain the car for her. I've given this a lot of thought and have told her to go buy a Toyota or Honda because service is close and inexpensive and these are very reliable cars.
I used to own BMW's (love 'em) and had lots of problems with them. Because of that, my wife won't let me buy another one. I told her that the parts didn't cost that much and that I was able to do all the work myself. Her answer was that if I wasn't around, she'd have to pay someone to do that work and wind up spending a fortune.
Mercedes in the past were actually quite easy to maintain if you did it yourself. Parts could be obtained at a discount from a variety of sources and the cars are superbly designed. However, if (like you) I had to take the car to a dealer for all this work I'd have to pay list price for the parts and as much as $90/hour to have the work done.
Having said all that, the major cost of car ownership is the cost of money and depreciation. What this means is that if you have a car that will last a very long time, it's worth spending money for maintenance and repairs because the alternative is to buy a new car and then you are going to get killed on depreciation, sales tax and increased fees.