I just tested this:
Select the affected books. Enter the bulk metadata screen and open the search & replace tab. Make sure the search mode is set to regular expression. Select 'authors' as the search and destination fields. In the search text field, input
and in the replace text field, input
Note the preview fields, which should show sensible author names now. Hit OK. Your author names should be fixed now. Check the author_sort values. If they aren't right, open up the manage authors dialog by right-clicking on the author category in the tag browser. Select to recalculate author sort values from author values. Now everything should be fixed.