If the CPU was cooled to handle any heat and the motherboard could go on forever then would the CPU just fail?
Like Geoff said, it's mostly a combination of the component's limits that forms the actual barrier of overclocking... as for:
probably not... sooner or later the limits of technology will be reached... i mean the chips were made to perform @ a certain level, they weren't made to overclock forever... the current limits of the technology you have is a definition of how far you can overclock...
you can't take a Pentium I and a Core 2 Duo and expect them to achieve the same clock speed can you?...