I'm going to say, no it will not be practical. At least for almost anything from the 16-bit era onwards.
Ideal case: you can get a datasheet on a chip and, assuming that the datasheet is correct and that there are no bugs in the chip, you can reimplement the chip. You do the chip foundary bit, or you use a programmable chip like an AVR to emulate the original chip. No huge fuss.
The next group of chips are things, like EPROMs, that are programmable. You can get datasheets here, for the chip. You may be able to get developer documentation on some of those programmed chips in some machines, but very few chips will be fully documented byte by byte. Which may be important if programmers used undocumented entry points. So if the ROM fails and you don't have access to another ROM (or a copy of its contents prior to the fact), you are SOL. As added fun, there is no particular reason why every used address in a ROM (or any address for that matter) has to be addressable for the CPU. So an image of the ROM made for emulators may not help.
Yet another group, well, they are programmable and have state information stored on the chip. (If I recall correctly, PALs and GALs fit in this category.) So it has the same issues as those EEPROMs and you cannot relaibly make a copy of that chip. At least, not without cutting open the chip -- and I don't know what you can determine in that case.
A final group that I can think of are programmable chips with internal security mechanisms. Mechanisms where, if a bit is set, it becomes impossible to read the contents of the chip. I've heard of this sort of thing for PICs and AVRs, but I don't know how common it is with older chips.
Ideal case: you can get a datasheet on a chip and, assuming that the datasheet is correct and that there are no bugs in the chip, you can reimplement the chip. You do the chip foundary bit, or you use a programmable chip like an AVR to emulate the original chip. No huge fuss.
The next group of chips are things, like EPROMs, that are programmable. You can get datasheets here, for the chip. You may be able to get developer documentation on some of those programmed chips in some machines, but very few chips will be fully documented byte by byte. Which may be important if programmers used undocumented entry points. So if the ROM fails and you don't have access to another ROM (or a copy of its contents prior to the fact), you are SOL. As added fun, there is no particular reason why every used address in a ROM (or any address for that matter) has to be addressable for the CPU. So an image of the ROM made for emulators may not help.
Yet another group, well, they are programmable and have state information stored on the chip. (If I recall correctly, PALs and GALs fit in this category.) So it has the same issues as those EEPROMs and you cannot relaibly make a copy of that chip. At least, not without cutting open the chip -- and I don't know what you can determine in that case.
A final group that I can think of are programmable chips with internal security mechanisms. Mechanisms where, if a bit is set, it becomes impossible to read the contents of the chip. I've heard of this sort of thing for PICs and AVRs, but I don't know how common it is with older chips.