In C++ code if you have an physics object / mesh whose class type is derived from UPrimitiveComponent (which it should be) you can call its IsAnyRigidBodyAwake() method. That’ll tell you the opposite of what you want, whether it’s awake.
For a temporary workaround you can add this line above the declaration of IsAnyRigidBodyAwake() in Engine\Source\Runtime\Engine\Classes\Components\PrimitiveComponent.h (around line 1694) and compile the editor to expose the method in Blueprints:
UFUNCTION(BlueprintCallable, Category = “Physics”, meta = (Keywords = “physics asleep sleeping awake simulating”))
This should be available in 4.14.