I'm sure the games still work. Cartridge games are durable. I'd be shocked if more than one of them didn't work after a good cleaning.
As for the value, you didn't provide enough information to even venture a guess. A lot depends on what games they are, the condition, and if the games are complete.
I would think on average that $2-$3 per game for loose NES games in decent shape for a big lot wouldn't be too terribly far off the mark. More if you take the time to sell things individually or in small lots. And more if you confirm that things are in operating condition rather than being untested. So I'd suggest taking a stroll down memory lane and keep some q tips and alcohol handy to get the more stubborn games going again.
Toss in manuals, boxes, and some desirable games and you'd be able to earn quite a bit more.