The rock walls, sushi bars and student center bowling alleys at colleges around the country will likely sit empty this fall. The spring semester has shown that online learning has significant limitations, said NYU marketing professor Scott Galloway, and welcoming back students and faculty is going to be like “Contagion 2.” But there’s also an opportunity here, he says, to increase budgets, cut costs and leverage technology to make higher education as accessible as it used to be.