Let's say Cinemark, Regal and other big theater chains around the US follow AMC in this stance. Who has the leverage now? Because at that point, Universal isn't getting shown in a single major theater. The theater owners don't mess around and never have.
I'm not saying they will, but IF the theaters stand together, then Universal is forced to play by their rules to be shown in theaters. It's not like there will be a lack of big movies next year either.