I honestly see it the other way.
We cant keep changing managers and DoFs, infact very few clubs change DoFs, unless they fail big time, see Walsh, Steve.
So unless Brands utterly craps the bed, he will probably outlast Silva.
But your also viewing it the wrong way, its a team, the football club should work as a team, its not about hes in charge or hes in charge, its about working as a team for the benefit of the football club.
As I said, currently Marcel Brands is the most important cog in the wheel, once the season starts Silva will clearly by the most important, but that doesnt mean they wont talk, ask each other for advice or even get advice when its not wanted. You are looking for division when in an ideal world there wont be any.
Brands will scout players, Brands will talk to clubs and Agents, once the season starts his role wont change, Silva will train the players, pick the players and shout at them loudly on a Saturday, Team work.