if he released it, he'd release EVERYONE he summoned, and then he'd have to go get the DNA again, which he said was hard and time-consuming enough the first time.I dont think if kabuto released IWR, the gin/ kin bros would vanish, because that means he could re-summen them in that way, which means kabuto could release every sealed character and re-summen them again, wich would make them invinceble AND anaffected by any seals.
Combine that with zetsu clones that can be made again(which would make them infinite) and madara / kabuto have an army of infinite untoucheble soldiers,
what do you guys think?
and with the Zetsu thing, they can probably create more, but it probably takes a bit of time. but then again, they got Yamato, which may not only make them stronger, but make the 'breeding' process go faster.