Can UAV with PX4 hover only by using IMU?

I’m new to PX4. Now I am using SVO on companion computer as external vision to upload the position. But the VO is easy to lose, maybe it is because of camera’s motion blur or something else. As far as I know, PX4 use IMU data as prediction, and others (such as external vision,GPS,optical flow) as obsetvation. Once there is no observation data, the EKF estimator should not be running properly. So my question is that is there a way could make PX4 drones hover/fly only with IMU? Or is there some method that could help drone fly stably when the external postion input is lost?