If Windows XP remains a major presence, as it appears likely, with projections as high as 33.5% of all personal computers at the end of April 2014, Microsoft could decide to continue patching the aged OS with free fixes for critical vulnerabilities, maybe even those rated important.
Such a move would be unpalatable to Custom Support customers, but Microsoft could renegotiate the fees -- unlikely -- or remind those companies of the program's other benefits, which include access to support representatives, as well as to prior patches and hotfixes.
Patch the critical vulnerabilities under active attack
Microsoft could selectively patch only the critical bugs that are being exploited by hackers. Presumably, that would be a subset of the complete XP patch collection assembled each month.
Some analysts have picked this option as a possibility. Last December, Michael Cherry of Directions on Microsoft posed just such a situation.
"Suppose ... a security problem with XP suddenly causes massive problems on the Internet, such as a massive [denial-of-service] problem?" asked Cherry at the time. "It is not just harming Windows XP users, it is bringing the entire Internet to its knees. At this time there are still significant numbers of Windows XP in use, and the problem is definitely due to a problem in Windows XP. In this scenario, I believe Microsoft would have to do the right thing and issue a fix ... without regard to where it is in the support lifecycle."
Charge users for XP patches
Although Microsoft would much rather book revenue from the sale of a newer OS, it may realize that some will refuse to upgrade, and try to make money rather than give away fixes.
It's unlikely that Microsoft would be able to charge $200 annually for post-retirement patches, as it does with Custom Support customers, but it may be able to get away with $50 a year for individuals and small businesses, perhaps with a maximum machine cap at, say, five PCs per customer.
Traditionally, Microsoft's not charged for support, but it could cast this as a special situation caused by the longevity of XP, which was due to the delay of Vista and secondarily, that OS's subsequent flop. In late 2007, when Microsoft extended XP availability to OEMs by several months, it cited Vista's delayed launch for the unusual move. (It added another extension in 2008 that kept XP alive on new "netbook" PCs, the then-popular class of cheap laptops, until mid-2010.)