it is here to stay.
they tried to go back to 100% on site working recently in my work and there was such an outcry from EVERYONE senior managers down that they caved in after 1 day and we remain flexible working.
I manage people in different countries anyway, so in terms of their interaction with me it doesn't matter whether they are chained to their desk, or sipping a cocktail on the beach, as long as they're getting the work done it doesn't matter to me.