What would happen if the sole pilot dies while flying an aircraft?
It has happened before that the single pilot lost consciousness while flying. What then happened is that the plane just went on until out of fuel after which it will glide down and skid to a stop (pilot survived). This is assuming there is no obstacle in the way.

Another example is the cornfield bomber, a fighter pilot eject and the plane still under power just kept going in a straight line and "landed" in a field.

A more deadly example is the helios flight 522. A mistake in the pressure regulation setting let the plane become unpressurized while climbing to cruise altitude. Both pilots lost consciousness and the plane's autopilot followed its programmed path following the waypoints and ending up in a holding patter until it ran out of fuel and crashed into the ground.

Survival depends on luck with obstacles, whether the plane is properly trimmed and which order the engines flame out in, asymmetric flame-out may result in a spin.