I think that history will show that this story has been shared in a misleading way.
Sainz Sr and Toto Wolff have no connection. It seems logical that Sainz Sr wanted to open negotiations for the Mercedes seat and Toto Wolff would not have any reason to discuss it with him unless he knew Hamilton was leaving. But of course this is speculation. Hamilton is 1 of 20 drivers on the grid. If it had involved a different name, no one would think anything of it.