Convergence doesn't need to go away. KDE project for example put some effort in making common components[1]. It's just that Canonical's methods of handling it went completely off on a tangent with reinventing the wheel (Mir instead of Wayland and so on). So it's not surprising, they finally realized the huge complexity of that task, and inability to do it alone.

No one stops others contributing to projects which still work on convergence, but use shared stack at the same time.

1. https://community.kde.org/Plasma/Convergence_Overview