Personally, I'd go talk to the guy and tell him the situation.  If he wants you to leave it for him to chop or harvest, then tell him you want to be paid on the 25 ton/ acre that the other corn yielded (assuming it is a comparable variety and looked comparable all season).  If he doesn't want to pay up front and isn't getting the silage made, I don't see where you are obligated to keep waiting, when he may come to you a month from now and tell you he's decided it's too dry to chop.  Just present it to him as a deal that needs to be finalized (he needs to pay) or you're going to have to harvest it because it can't wait any longer.

If you talk to the guy and present your case, I don't see how there can be a problem. 

Good Luck,

Mike