autossh appears to fulfill my requirement, from the readme:
autossh is a program to start a copy of ssh and monitor it,
restarting it as necessary should it die or stop passing traffic.
Substituting the arguments given in the question:
autossh -M 0 -L 8080:localhost:8080 example.com -g
-M 0 is required to turn the
monitoring loop off)
I was able to
kill -9 the connection from
example.com and see the connection re-established automatically by
local$ autossh -M 0 -L 8080:localhost:8080 example.com -g
Last login: Wed Apr 25 03:23:56 2012 from 203.0.113.123
kill -9 on PID of connection on
local$ Connection to example.com closed.
Last login: Wed Apr 25 03:34:01 2012 from 203.0.113.123