If the error was detected before the first pitch to B8, B8 would have been declared out for failing to bat in his proper turn after B7, and if there had been less than two outs, B6 would have been removed from first base.
B9 leads off the next inning.
If the error was detected after the first pitch to B8 but before his at bat concluded, B7 would have batted again--why? because he follows B6 in the batting order--and he would have assumed the ball-strike count at that time.
Don't worry about a distinction between completely skipping a batter and switching places. There isn't one. B6 stepping in after B7 flied out was just a second instance of batting out of order. The first instance was nullified by the first pitch to B6.