Nothing will happen with any of them until you get them into better conditions. Just harvesting the plant and cutting off the top half is not going to fix it for you. The plant will not survive unless you can fix the problem. (and even then only if you work fast and are VERY lucky :wtf If you still have any of the above issues (poor soil, too much nutes, or poor drainage) you are still going to lose that plant for sure.

I would doubt that a half grown seed is viable but again.....why not try? I certainly wouldn't count on it to germinate but what harm can come from giving it a go? I think you are are going to need new seeds though......really doesn't sound like you have any usable ones there.