One player a season is moved on at the height of his value and is usually replaced with as good or better for much less £ (with the exception of Mahrez).
It's a bloody brilliant system. You're perfectly pitched to do it as well, and the football you play makes the best of your players so they always go for top whack.
Leicester are great at buying and selling players, and also holding on to the key ones like Vardy. And very good at playing football, too.