XP will become like Windows 95 and 98 where they still operate as they currently do, but there will not be the usual monthly updates and patches given out by Microsoft.
There may be (as I would expect) clubs / forums that offer specific help related only to XP, since it still has many millions of users, but there will be nothing from Microsoft itself once the decision is made. They (we) will still continue with using our systems as they are, but you will just no longer have the support that was offered.
I have 3 former XP based units in my shed that are now going to the garbage, as I stripped any good parts, and they are now Old Worn Out Wrecks - -
Thank You -
P.S. There is / was an expected life span of these systems and most have passed that date -
Did you know a Mouse was originally designed to only last 2 years ?