This nut is a nylon locking nut and I must wonder how it loosened. At the same time the bottom bracket also seems like it should be tightened but I've choosen not to open it unless the nut actually comes off.
In tightening this nylon locking bolt it is important that some small portion of the bolt be showing through the nut to be sure it has engaged the nylon locking portion.
The housing was replaced easily by pushing each of the four spiral grooved brads into place then tapping home.
The assist handle feels solid again.