Destroying Soul Society would involve the eradication of the Souls that live there and the murder of the 3000 or so Shinigami who reside within Seireitei. If that happens, firstly Plus would go utterly unprotected and Hollows would multiply exponentially without Shinigami to keep them in check. Also, Plus would not be konsoed and so not come to Soul Society. In addition, with the Souls in Soul Society being destroyed, the circle of reincarnation would break down. So, literally, the world as we know it would be destroyed.