I have 300+ ounces in my deep freeze. My twins normally nurse first thing in the AM and before bedtime, and get pumped MM during the day (I pump after the AM nursing before going to work). I accumulated some reserve early on when I pumped all the time, and from when I've had to go out of town for meetings and froze what I pumped. And now I'm separated from my husband, so when the twins have overnights w dad I pump and freeze the nighttime MM but leave the morning's pumped MM for when they come home.
I've broken into my stash a few times -- when my twins had a GI infection, or otherwise weren't feeling well w a cold. I rotate the stash, so I use older stuff first. I have no intention of ever throwing it out unless it goes bad. With our first DS (too weak to nurse), I only pumped about 5 months, but the excess lasted a full year, and then the small amount left because the electrician forgot to plug the deep freeze back in after a repair. Incidentally, I now use only Lansinoh bags because I never spill them, but then I used whatever was cheapest and never had leakage problems.
If they wean before I've used it up, they would probably sitll want to drink it. If not, I would cook with it! Our nanny has made bread pudding, pancakes, rice pudding, oatmeal, and a variety of other treats for the kids using my MM. (I do not have a huge supply, but early on I pumped enough that at least for a while I had more than they drank.)