This is all just extra complexity:

1. Just have the notifier's stop close(n.pendingNotifications).  When this thing is told to stop, whatever is in a state to continue sending events should stop as well.  The notifier shouldn't know any better.

2. Have this run a for { } over pendingNotifications.

It will automatically drain on close.  Explicit state management is just extra unneeded complexity.  The more idiomatic we do this, the simpler the code will be.