They are hard but not solid, when I moved them they broke in the middle but didn't bust the bags.I would like to use it to set some posts but I'm not sure that it would mix well. May be lumpy and insecure?

I hate to just toss them.

If it breaks up into small pieces you can mix it with fresh concrete, but big solid lumps have pretty much gone to concrete already. Probably OK to use for setting posts, but any kind of critical work like a foundation, you want fresh concrete.

A construction worker buddy of mine just explained to me last week that chunks of concrete act like gravel aggregate when mixed with fresh concrete. They don't behave like concrete. In other words you're kind of diluting the fresh concrete with extra gravel. But he's used those half hardened bags exactly the way you propose - for posts. Mix with some fresh concrete and it should work OK.

Dry concrete mix is always stronger than wet and gloppy, BTW.

i would store it and reuse it in a new batch i had no problems like i said reusing it all i had to do was break it up which took very little effort for how hard it was.

It incorporates the water into a new compound and that's what makes it hard, and that's also why it's hot when the reaction is taking place and you can get burned by it or by plaster of Paris or similar things. Once the bags are wet, the water has been incorporated into the cement. Mixing that with new concrete and water is like mixing rocks with it. For setting a post, it's OK because the ground is going to be the stabilizing factor. But you should never build with it because it's going to be structurally very weak.