Devices break. Every device eventually will wear out or fail.
Nikon's F series are extremely robust, however, which is why they have been the traditional choice in SRLs for legions of photojournalists for the past half-century. When last used some four years back, my F3 was starting to darken the right side of the frames - obviously a shutter problem developing.
It is now a bit over four years since I bought my first digital camera, the Nikon Cooplpix 990, replaced by the CP5000 about two years ago. Now realize that these cameras make no pretense of having the F-series' robustness. They are high-end prosumer cameras and not made for the rigors of daily photojournalism in the field. None the less, I have had no problems whatever in the tens of thousands of shots over the past four years.
These cameras have completely replaced the Nikons and the Leicas. However, for top quality I still shoot medium format - as manual as you can get. There too, shutters in lenses need maintenance. A few years back all three lenses for my Linhof technical camera went for cleaning and calibration, and I just picked up my 150mm Bronica ETR lens after the shutter stopped working.
Manual is no guarantee of robustness, nor are complex cameras necessarily less reliable. The little Nikon digital cameras have allowed me to shoot in situations I would not even think of were I using film. Once you have conquered their formidable learning curve, incredible possibilites present themselves to you. In all my decades of photography, nothing has even approached being as liberating as digital.
Digital and medium format work beautifully side by side. Everything I would have shot with 35mm in the past is now shot digitally. Any time I travel, do architecture or epic landscapes, I have my medium format arsenal. Yesterday, I was shooting with both my digital and a WideLuxe 140Â° panoramic that uses 35mm film, but shoots a negative 6cm wide.
I use Epson's breakthrough scanner, the 4870 for panoramic and medium format images and the prints are superb. Finally a flatbed that does film quite well. With digital and the scanner, I have complete control of all my images from concept to presentation, no matter the source. My prints are only distinguishable from those I made in my colour lab years back, by the fact that they are so consistently good. A run of the mill first print from my digital darkroom is the equal of a portfolio print I spent a day making back then.
Your piece of mind is very costly. You have both missed many images and much pleasure by restricting yourself in this way. Much has happened in photography in the decades since the F2 came on the market, and these instruments greatly extend one's reach in image acquisition.
I shoot with the highest of tech and the lowest of tech - each has its place. Check my web-site and I am sure you will "get it". Obviously, these images are not the product of a worried mind. The choice of camera is not dictated by whether the thing will break on the shoot, but by the needs of the subject matter - which is the ONLY consideration.
I also sleep very well, indeed no matter what I shot with on a given day.