I don't think they will.
However, slowly but surely there'll be the odd user here and there who'll find their XP machine doesn't work quite right.
So situation normal then.
The end user, not knowing their arse from their elbow, will chastise the IT guy for not making it work, and will dismiss the counter-argument of XP being inherently flawed from that moment on as unproven.
Again situation normal. And has been ever since we moved away from terminals onto mainframes. Well to be honest it was like that before then even though I only saw the tail end of them getting removed out of service.
It'll therefore be a slow-moving mass of pain to a greater or lesser extent depending upon how much reliance is placed on the system by the end-user
I would say extremely slow moving as the majority don't actually use them for much. If they were high end users they would have upgraded their hardware years ago.
Only way your going to stop people using it is if you make the OS useless for general use.
ie . Change the major web sites such and search engines, social media, mass email system refuse connection and be unusable to XP machines.
BTW I just finished work and in the course of this morning I came across 8 XP machines.
Then again there are quite a few NT4 machines still kicking around and nobody makes a fuss about them. But then again the numbers will be low enough that nobody can be bothered doing anything to stuff them up.