Can the VIO signal be disconnected while VCC is powered up after Flash enters Standby Mode, Auto Sleep Mode, or Deep Power Down mode?
Yes, but this is a datasheet violation and is not the best practice.
There is no risk of damage to the Flash when VIO is removed when the Flash is in any powered state. However, doing so will cause the Flash to enter an undefined state, and may not reduce power consumption. The recommended recovery from the undefined state is power-on reset (POR).