Remember that Intel was twisting arms and making deals to kill the weaker RISC chips in the marketplace. In the leadup to the first Itanium, HP had acquired Compaq (which had acquired DEC), so they held both Alpha and PA-RISC. And SGI was still a fairly big player with mips64. Both HP and SGI made deals to use Itanium going forward (with HP going so far as to port HP-UX and VMS to Itanium).
I think the server marketplace would probably have been much higher margin without amd64 competition, as itanium was always a high margin player. Its main competitors were the high margin server chips above, plus POWER and SPARC. The low end was x86 controlled by intel, and they could certainly continue to artificially segregate the market and keep margins high. That's what they were good any monopoly does, and what they've been trying to do today with Xeons.
I was a huge fan of Alpha (one of 2 people who ported FreeBSD to the alpha), and I was very sad to see it go. I've always blamed Itanium for its downfall -- I think Alpha had a lot more headroom than PA-RISC, and HP would have kept it going if it were not for Itanium. So I have to admit that I'm quite happy to see Itanium die.
SGI is interesting because they _owned_ the 3D space and shortly before he went to Microsoft, SGI gave nVidia and Microsoft very cheap licenses to their extensive collection of patents and other IP. It's interesting to imagine what might have happened if, say, SGI had switched to Intel but with fewer gambles on unproven technology: x86 and Linux or the internal IRIX x86 port instead of Itanium and the heavily modified Windows NT derivative which was very expensive to support and forced all of their developers to make massive code changes. Similarly, they were focused on the high-end 3-D market (engineering, science, animation, etc.) and dismissed the PC gaming business as insignificant and basically gave it to nVidia along with a bunch of their staff; had someone a little short-sighted been involved that would have made a big difference in their bottom line.
Also, had it not been released, we'd probably have seen a larger fracturing of the laptop CPU market with a broader switch to ARM64.
In a sense, because AMD forced Intel's hand in supporting x86_64, they actually helped Intel have even more dominance in the market with an architecture that spans laptops to server work horses. We developers barely need to lift a finger in targeting either.