If you ever tried to use rock salt from last year you will find it's a large block of salt now. I would suppose it depends on what the bearing surfaces are made of. It's possible the surfaces could start to form corrosion/rust but i think you would be able to see that. I remember years ago when TRW made bearings they where individually sealed and placed in a cardboard holder so they couldn't rub against each other. Ever look how Mahle bearings are packaged?