• Support for XP is ending.  Without support there will be no more patches for newly discovered vulnerabilities. Without patches there will be exploits in the wild for which there are no defences.  Without defences, it would be hard to show due diligence for compliance and without compliance, you'll soon loose business.  As this specific case is a problem with XP then any proposed solution cannot include XP.
• You may well have some applications which are only compatible with XP as there were many changes in Vista such as tighter security which can break poorly written applications.  In principal you could move them to Windows Server 2003 (R2) and access them via RDP.  This might give you another year's grace but it's far from ideal.
• You may even have some hardware devices for which there are only XP drivers.

So if the problem is the desktop operating system and anything critically tied to it, then the traditional way forward would be to upgrade your desktop operating system.  Along with hardware, drivers and applications as required.

But this 'upgrade treadmill' is only a short term fix as Vista, 7, 8 etc. will also reach this point again and again.  Each time requiring more investment and more re-training.

Cases have been seen whereby each user has a full Windows 7 PC just to access their cloud desktop. The underlying full desktop PC still has all the expense, licensing, vulnerabilities, maintenance & life-cycle issues as they have had before.  Except now, all of the users' cloud applications become unusable when they loose the bandwidth battle as several PCs fetch their routine updates at the same time.

Some perceived advantages of a cloud solution are actually just the result of a more tightly managed desktop.  Because it is often presented as a new and different way of working, users seem to be more willing to accept restrictions of what apps they're given and the fact that they can't fiddle with distractions.  They're also more likely to be using shared departmental printers rather than getting one on each desk.

But these are all things that were normal years ago.  Somehow, we've slipped to a point where users feel unfairly treated if asked to cut back on their Facebook usage.  And why does anyone have games or even WinZip on a workplace desktop?  There's still nothing wrong with the desktop paradigm if well managed.

Perhaps then, the inevitable pain of unavoidable change should be borne with a greater pay-off in mind:

•  Get back to a tightly managed desktop workspace, even if it's hosted within a Bring Your Own Device (BYOD) environment.
  
•  Thin client devices to replace really old PCs, increasing reliability & reducing power consumption.
•  Thin client software on repurposed PCs, replacing Windows with a minimal, hardened OS & browser.
•  Remote access to line-of-business applications whether Windows based or otherwise.
•  Using Software As A Service (SaaS) from external providers who manage the application.
•  More use of Open Source Software for better control of updates, upgrades, licensing, compatibility.

The latter alone can be a major step towards a more comfortably sustainable long-term IT environment as Open Source typically follows the “little and often” approach to updates & upgrades.  Even Microsoft are beginning to move in this direction with recent announcements of smaller annual updates rather than the trauma of a big-bang every three years or so.

Note that the application services and servers could still be in your own IT room or a cloud services provider.  Most of the pain in traditional IT systems is experienced where the users are, not the servers.  Moving the services to a cloud won't necessarily help.  Changing the users' experience will.