XP is not going to stop working just because Microsoft say it is no longer supported after a certain date.
And I would imagine that if any major or severe problems turn up in XP then Microsoft will still fix them.
I would just carry on using XP until you reach the point when the PC is just so old you can no longer continue using it.
The biggest problem you may find is that as new technologies come along then XP will not have support for them, so it will gradually become isolated.