Nico Rosberg retires form F1 — I didn't expect that!

[SteveB]

This will upset the apple-cart with regard to other teams.
Who will replace him?
Do Mercedes want another driver to rival Lewis, or a “number two” driver?
“Number two” drivers, like Eddie Irvine, who just want the money and are happy to act as a “rear gunner” and drive “the wide car”, are less common now.

Imagine the good racing if Fernando Alonso or Sebastian Vettel moved to Mercedes.