The planet seemed instantly recognisable as Mustafar. How many people who wouldn't have recognised the world would have known the name?
Plus, Vader features very promenantly on the poster.
Rogue One's only way out once the battle on the beach started would have been to blast their way out and they stood no chance against those StarDestroyers at the gate. They pretty much went in their without an escape plan. Realising they were trapped was pretty much Jyn and Cassian just accepting that.
Plus, sooner or later a commander on one of those Star Destroyers was going to find out about the fighting on the surface and inform Tarkin. And I'm sure Krennic would have ordered the shield gate closed
The fleet attacking simply brought Tarkin sooner. Also, he team on the beach were done for against the walkers until Blue Squadron showed up.
So Raddus did save the day.