The NG handles well in low speed high angle of attack scenarios. For a NG to end up in a situation with near full AND trim (a situation where manual trim wheel operation is not possible) you need an unnoticed runaway trim for quite some time.
I have trained runaway trim in the simulator. A nose up trim is harder to notice since STS trims nose up, but you can turn the trim wheel manually in this situation.
A trim down will be noticed long before you get full AND. The runaway trim QRH procedure takes care of this problem.
The NG is safe.