spool engines eg:TPE-331 have the flight idle fuel flow set high enough to prevent negative torque from occurring when the propellors reach the low pitch stop
Its also to note that that torque setting produces more drag than feathured, most experenced crew want the flight idle tourque set as low as possible about 2% is good for me. Inexperenced crew hate it low and prefer it up at 8 percent.
If its goes below 0 and there isn't a NTS system fitted the plane basically stop in the sky. 250knts down to stalling in a Nm in level flight. And can get very interesting especially if your in a turn and the inside engine is the one set to low. You get a huge leans effect and it feels as if the wing has grounded on something and the whole aircraft is rolled and yawed into that side.
Also as well the props that are usually fitted the hub is controlled by oil pressure and a big spring. As big as that spring is if you get into beta range its not strong enough to return the props into Alpha in flight due to the aerodynamic forces. Its happened a few times over the years and the plane has been turned into a brick with everyone killed.