Indications
If I recall correctly, the Lauda 767 did have a number of issues with its reverser on previous flights, indicated by (intermittent?) REV ISLN (reverse isolation) light.
Also on the accident flight, the REV ISLN light illuminated intermittently.
Position of reverser is properly indicated on engine instruments, probably on every aircraft type, by "no indication" for stowed, amber "REV" for in transit, green "REV" for deployed. In case of uncommanded deployment, warning display may trigger an alert (depending on aircraft type).
For chance of recovery - at low altitude, low speed, high thrust, chances are dim, lack of maneuvering room. At high altitude, improper reaction may come into play: unfamiliarity with unusual attitude recovery (civilian flight training conditions people to maintain positive gee and to pull to get back up to altitude; in case of severe roll this will lead to a pull through the vertical down, which will invariably destroy a jetliner. Proper reaction would be to unload, roll back or roll through, but keep the nose from dipping down too deep).
Many informative postings prior to this one, compliments.