I found the picture humorous, reminded me of so many post holocaust games, unfortunately it also reminded me of some cities I passed through that border the Ohio river.
Post-holocaust is perfectly correct. The event of nuclear war is often refereed to as a nuclear holocaust. Note the lack of capitalization on the 'h' making it not signify the proper name for the event, the Holocaust. http://en.wikipedia.org/wiki/Nuclear_holocaust
"a great or complete devastation or destruction, especially by fire" - sgtm
I'm glad I'm not the only one who has to do something when someone corrects a person, but is wrong themselves. One of my BIGGEST pet peeves!
I would still bet the OP actually meant apocalypse, even if their mistake turned out sorta correct. "Post-holocaust" is a rare usage.