The slow performance would eventually have lead to Intel realizing its bad idea. They would use market share to competitors on different ISA.
Windows at some point would want to be on faster processors and would again run on some of the others. Windows doesn't have undying loyalty to Intel.
Other people then AMD could do a x86 implementation with some 64 bit overlay as well. Transmeta style. That kind of system would beat Itanium as well if it was put on top of a fast RISC processor.
And at some point AMD even on 32bit would massively gain market share as they invested more in faster RISC style processors. So Intel would have massive pressure from the bottom end and the top end. And in any possible future AMD at some point it gone do something with 64 bit.
The idea that the whole industry goes massively backwards and stagnates for years because Intel monopoly doesn't really work in practice.
The point is that NT is portable, and once Merced hit the market in 2001 5+ years overdue and not delivering on any of its performance promises, the only question was "What architecture will succeed x86, because we can cross IA64 off the list." In the same way that when the 432 showed up years late and 5-10x slower than a contemporary Motorola 68000 or 286, the 432 was dead in the water and all the early 80s workstations were built with 68ks and the PC market went with 286s.
I don't know if the absence of AMD64 in 2003 would have made an opening for SPARC or PowerPC or ARM or something else entirely, or maybe the "Let's slap an expansion on the 8080 again, just like the 386 bailed use out after the 432 debacle" scenario was inevitable, but NONE of the compiler-scheduled-parallel architectures panned out in the market, so someone else was going to win.
I have read one insider account that Intel had its own, different x86-64 instruction set, designed in response to AMD's. It approached Microsoft and asked it to port Windows to it.
Microsoft refused, saying "we already support one failing 64-bit architecture of yours, at great expense and no profit. We're not doing two just for you. There now is a standard x86-64 ISA and it's AMD64, so suck it up and adopt the AMD ISA -- it's good and we already have it working."
Or words to that effect. :-)
I've not been able to find the link again since, but allegedly, yes, the success of AMD's x86-64 has been due to Microsoft backing it. It sounds plausible to me.
