That could be possible, but it goes against the "God doesn't waste His time on people He knows won't stay saved" theology that some have.
i'm not sure either to be honest.
demons do in fact leave people on their own, no exorcism needed. i suppose this might be rare but if a person turns back to God after the demons leave, they will be fine. when they don't, that door remains open.
Jesus speaking parables concerning "this generation" which initially did sweep clean their house, accept him as he rides into jerusalem on a donkey.. then 3 days later they kill him. (or the next year depending on how fast you think all that could happen) --we should probably not invent theologies from parables.
now as for kingJ who doesn't understand what the waterless places are... its the place demons exist in, unless they have a person to inhabit. Its the so called second heaven. there is no "water" or "rest" in that place.
ever notice old folks suffering from dementia, their problems leave for a week or two before they die, and their previous evil demenors return to average to good behavior?
science has no explanation for it.. but i do. the demons left them because they knew the person was about to die.