This comment expresses almost exactly how I feel about the ending of the series. I was less horrified by it being Aoi, mostly because I'd been suspecting Mariko and I adored Mariko; I was so relieved that she really was as awesome as she'd seemed in the previous episodes that I was less distressed over the Aoi angle. But, yeah, I also have my doubts that Shuuji would have been all right without one of them to ground him. And, like you say, the fact that it was Nobuta's idea goes pretty far towards reconciling me to the idea of Nobuta being left behind.