I think the chemicals dry out. I've not tried with integral, but have gotten old Polaroid Type 47 rollfilm on ebay - about 40% to 50% of it worked, though not like new. (Oddly, I've had better luck with the ones that expired in the 60s, and worse luck with mid-80s vintage.)
Don't try to take any important photos with old instant film, just in case it doesn't work.
I've not really tried what you have, but if you have a meter (or a flashlight and a couple wires) I'd just test the battery pack before attempting to move the contents into an Impossible cartridge. Those batteries were pretty robust.
I ran across one of my old father's Polaroids (sonar, one-step style) about three years ago, and it still had an empty cartridge in it. When I powered up, I could hear the flash charge just as fast as a new Impossible cartridge would do it. It had not been used since the late 1980s (possible 1992, but no later than that).