Until a cause and a cure are found for SCLS, yes, no matter what effective therapy you receive to prevent new episodes, you will need to receive it indefinitely. Otherwise, you risk a comeback of the episodes -- and just one of them can kill you, so you'd be playing the equivalent of Russian Roulette if you got off of IVIG. You are stable as long as the IVIG you receive has not been lost or degraded, which happens after 4 weeks; however, you are by no means cured.
Some kinds of nerve damage can be repaired with the passage of time, and other kinds cannot. For example, if you put pressure on a nerve for days or weeks, it may well recover once the source of that pressure is removed. In contrast, if a nerve is cut or dies, it is unlikely or incapable of repairing itself.
I experienced extensive nerve damage and nerve death in all four limbs during my first episode. Some of the damage was repaired; most was not. And the dead nerves, of course, never revived.
As to orthostatic hypotension -- perhaps you have the most common symptom, which is feeling lightheaded or dizzy when you stand up after sitting or lying down? -- it may or may not be related to whatever damage you sustained as a result of a capillary leak or the attempts to revive you. It can be caused by many different conditions (dehydration, heart or endocrine problems or nervous-system disorders). To my knowledge, it's not a common complaint among SCLS survivors.