Yes without humans, or other beings, maths is not very useful , but the same applies to physics.

You're taking this analogy a little bit too far. The laws of maths are true and exist regardless of the existence of humans. I'm just giving an example.

Lets say maths is a robot then physics would be like one of the modules that tell it what to do, i.e: giving it missions. There are many of these modules and without anything to do maths would be not very usefull but then again the module without the robot is just as useless.
Even if one of the modules is taken down, there are many more modules (i.e: economics, chemistry, biology, almost everything) that uses maths. If the robot disappears however, the module has nothing to do since there is no substitute to maths. You can't find another way to calculate stuff because the calculation of stuff itself is maths. (amongst lots of other applications)