There are several ways to respond. They include I don't have a working radio but I need to land now. Control towers know these procedures exist and will look them up when needed (they are used so rarely that nobody remembers them). So long as you are acting like a pilot who in an emergency you will be fine in general. (of course if you are acting like an emergency in a way that would allow you to pull a 9-11 attack on something important they will shoot, but it isn't the default).