What RJ intended or not at the time is quite irrelevant in this context. The rules were eventually made up, and that scene of EOTW has to be interpreted in the light of the transmigration limitations introduced later. If that scene violated the rules, RJ would have gone back and tweaked details in new editions to make it fit (as he's done in a few places through the series)

There's little doubt that when he wrote TEOTW he wanted to leave the issue of Kari's reality open for the reader. It served his dual purpose to offer a satisfying "stand alone" ending while not tying his hands for the rest of the series. Was Kari's reality an open issue to him, though? That's another question, but I'd say probably no more than Ba'alzamon being or not the real DO in his mind. It's pretty clear in EOTW that the concept (explained only in later books) that reality in TAR is shaped by your will or a contest of wills between opponents, and you need to deny this reality to undo it was already existing in his mind at that point. Of course, by EOTW RJ was the only one who knew anything yet about his world of dreams.