If the writers substituted the whole "ripped out of heaven" subtext for the season with a new "just had to stand by helplessly while my little sister died" theme, substituting the sense loss of a loved one for the loss of Eternal Rest And Reward, they would have been able to pretty much keep Season 6 intact just as it originally was, especially if it was Buffy, and not Angel, who retreated to a temple in the mountains for the summer, leaving Spike and the Scoobies to take up the slack on the hellmouth. There was very little, if anything, of any importance that Dawn did in Season 6 or 7 that couldn't have been done just as easily, and in a far less irritating manner, by Willow, Xander, or Giles.
And, as an added bonus, not one single, "Get out. Get out! GET OUT!!!" for the entire season or ever again.