but isnt the current management and creditors the people behind all the corruption?
Current management, allegedly. Civil rehabilitation exists so they can put a plan (anything from a relaxed payment schedule to payment in stock to court-appointed management) before the creditors and the court to keep Index on the up-and-up.
This doesn't necessarily mean Index is in a great position (the lead creditor could be a bank that wants their money back now and is willing to make nothing but Persona-themed compgacha to get it) or that it's in a better position for gamers than liquidation (which could see Atlus go in one solid chunk to another publisher.) Just that someone thinks a court will say "this is a decent business proposition that did something dumb and needs some breathing room" rather than "it's fucked, carve it up".