There's a chance. Obviously it's a very small chance though, or we wouldn't actually hold onto him.
But you can't predict plateaus. A player who is and will continue to improve looks identical to one who is improving but will plateau as this new season starts. If Zaha plateaus this coming season, showing no improvement on last, his value would fall back. Suddenly all that potential to improve is gone and with it a large portion of his value, and the 5 or 7 million pound offer from mid low-mid prems teams is replaced by maybe 1 to 1.5 mil offers from other championship clubs.