Here's the problem with returning the runner. What runner are you going to return? S/he's no longer a runner because, by rule, THEY have already been declared out.
ASA Case Book Plays 8.8-15 & 8.8-17 notes that even though an over-the-fence HR is a dead ball, runners still may not pass each other and the passing runner will be declared out. That settles the live/dead ball discussion.
Now, the question becomes the fair/foul issue. Since no runners may advance on a foul ball of any sort, I believe a passing runner should not be declared out. Therefore, I will offer the following rule change to ASA for the 2007 season:
Runner is out
Add 8.7.D
EXCEPTION: When on a batted ball which is declared foul
Affects POE #39