I think McVay is one of most stringent 'follow the game plan' coaches in the league, if not history. I think he looks at an opponent and thinks, "Here's how we beat this team"... then spends the week putting together the plan. Game time it's 'the plan'.. come hell or high water. It's been a VERY successful strategy.
To repeat... I dunno.... but I think McVay game plans this next game no differently than if Williams and Rivers were active. There is a 'way', in McVay's mind, to beat the Steelers and no matter the player on the field they will adhere to that 'way'.
So we may see few runs, or lots of runs, but either way I don't think it will be indicative of any 'change' in McVay's strategy due to Williams and Rivers, or any other player, not being available.
A good example, to me anyway, was Nacua without Kupp. Nacua became Kupp. The strategy didn't change; and that with arguably the best WR in the game on the bench. - JamesJM