They're incredibly rugged cameras, being designed for Press use. The bellows are usually two layers, and stored inside the box, so they tend to hold up well. Doesn't mean they don't deteriorate, but if they were reasonably well cared for when put away, they should last forever.
My Mini Speed (1946), according to the seller, was bought from a photojournalist and given to the seller as a present for his 16th birthday, in 1963. In 1970 or thereabouts, he switched to 35mm, and forgot about the gray box marked "Graflex" in the back of his closet. In 2020, I bought the whole crate from him, and while every glass surface needed cleaning, the rest of the camera (and accessories) were in perfect working order, and both shutters were within 10% of spec on shutter speed. This is probably atypical, but it should give an idea of how well these things hold up.
Parts and spare bodies are reasonably plentiful, and there are a handful of techs out there who can work on them, up to and including servicing the focal plane shutter. The shutter mechanism is fairly industrial, but the springs are the weak link-- if improperly stored, they seriously lose tension. If properly stored, they still lose a bit of tension, but can be re-tensioned (and lubricated) relatively easily.
I suppose the other questionable bit would be the set screw for the rangefinder adjustment-- One or two people have reported them slipping, and I've noticed mine was a bit out of calibration after being stored for a few months.