Doubtful. The only way iPad full replaces the "PC" is if the iPad processor is switched out to an Intel x64 and iOS is fully dumped.
Maybe I'm ignorant, but I just don't see a ARM processor and an os built for "productivity" (read: email, Internet, word processing) being something that will lead the PC to extinction. Engineers, developers, graphic artists, and anything with high end processing will keep PCs alive for years.
One other note: when Steve Jobs introduced the iPad, he presented it as the in between the smart phone and the PC. It simply was never meant to replace PCs.