If you buy a new computer, you won't have a choice. Dell is forcing Windows 8 on everyone.
Go to your local software store and see what the oldest Windows software you can buy is. Can you get new software for Windows 95? The answer will probably be "no". Pretty soon the stores will stop selling software for Windows XP and your answer will be "Windows XP is broken".
The other issue is length of life on hard drives. They have surface mount components and they don't all last beyond 5 years.
What forces you to use W8 on DELL computers? I suspect you are talking about laptops since most enthusiast computer users put together their own desktops, but sure OEM laptops will move to newer OS but you can still format the drive and install whatever OS you want as long as there is drivers available (currently not much of an issue) also who buys OEM desktops?
Also due to the limits of the 32-bit kernel in Windows XP you have no real reason to buy a brand new laptop to use Windows XP on as long as there is working second hand ones.
What is the issue with hard drives? Are you talking about hard drives or solid state drives?
Since I got tons of more then 5 years old hard drives running 24/7 in my file server without issues, the biggest killer of hard drives is heat which is a problem for laptop users.
Running old software on newer OS is no issue, I use VMware to run DOS and Windows 3.11/95/98/2000/XP etc and run all legacy software I want without trouble, you can use whatever virtual box you want for that but VMware is Superior on many aspects and have DX9 support.
Besides software using later DirectX version (mostly games) than you can use on Windows XP much software will still run under Windows XP for quite some time, the gap between Windows 9x and NT based are mostly caused by the move to the NT based kernel of Windows XP so such dramatical compability issues will not be as apparent between XP and 8 before the leap to 64-bit software kicks in.
So I still do not see the issue, if you want to run unsupported legacy software you can, most things will run for quite some time on Windows XP still.
The biggest problem I can see is when new hardware do not get drivers for Windows XP but it wont be an issue since the Windows XP kernel is getting more and more outdated for new hardware anyways so XP wont be optimal anyways and if you want to keep using it you could run it trough virtual box or keep XP supported hardware.
Since there are already limited by the 32-bit version of Windows XP from both new CPU pov and the limited RAM capabilities including VRAM (not counting the broken 64-bit version of XP with very limited driver support) you will be forced to move to a new OS by time but only if you are in need of hardware not supported by XP.
So yes, Windows XP will die out due to new hardware and higher software requirements by time, but nothing stops you from running it on a VM or keeping XP supported hardware for a XP computer.
So bottom line, XP is a decent OS yes but getting to old, nothing stops you from using it for quite some time, if you are not limited by the 32-bit kernel keep using as long as you want.
But it will be outdated as time progress but I predict most software will keep running for quite some time on it.
Getting outdated, yes.
Dead, no since it depends on the user.
WOW, i wrote a lot of text here, hope it's understandable and not to much off-topic
Edit: Also as it looks now with possible release of Windows Blue this summer with cheaper more frequent upgrade releases it seems Windows won't get better and I hope to god Linux will rule the desktop market in 5-10 years time due to Microsofts new approach!