Re: I would imagine at that age bitrot would be a problem, no?
The PROMS are bipolar "fused link" type, IIRC. There have been cases of such fuses "re-growing", but not many. They were used in many arcade machines of the day, and many of them are still running fine. "re-flashing" these parts, or even putting them in a modern hobbiest PROM reader/burner, would be a very bad move. The hard part of restoring (or counterfeiting) an Apple I is the shift registers used in the CRT controller.
One major issue you might run into is the high-resistance eutectic alloy formed by prolonged contact between gold IC pins and tin sockets (or vice versa). When I ran into it, circa 1977, my research found that mainframe manufacturers had run into it in the 1960s. For an industry that talks so much about "memory", computing seems to be willfully amnesiac. Fortunately, the "folk cure" of rocking the chips in their sockets (or removing and replacing them) will buy you another several years. Minus the damage caused by over enthusiastic application of the fix.
("IIRC" above refers to my not wanting to bother to find my Apple I manual. No, I never had the machine itself, but do have a manual. The PROM implements a small 'monitor' for the equivalent of PEEK and POKE. It is 256 bytes, again IIRC)