Banding is an instant ability and since abilities on characters activate when they enter battle, you must band at the start of battle or not at all. You can't decide to use the banding ability later. Also, in the case of special initiative, the only thing you can do is play an enhancement that interrupts or negates the ability causing the removal. In addition to that, heal abilities only work on characters who are already being discarded and during SI the discard ability is suspended and hasn't actually happened yet so trying to heal during SI wouldn't even do anything.