After doing apt update and apt dist-upgrade of Xubuntu 16.04, the nm panel plugin seems to have disappeared, both from my panel and the list of plugins.
Note the lack of Network Manager.
(Networking still works, though.)
Contents of ~/.xsession-errors:
[email protected]:~$ dir .xsession-errors
-rw——- 1 ron ron 153 2018-02-03 13:38:20 .xsession-errors
[email protected]:~$ cat .xsession-errors
openConnection: connect: No such file or directory
cannot connect to brltty at :0
upstart: im-config pre-start process (2085) terminated with status 127
The timestamp is from when I last logged in.