I wouldn’t be so sure that the Brewers won’t be using any of their top starters at all in the final series even if the division race is decided.
Burnes, Woodruff, and Peralta are slated to pitch this weekend, so if they stayed on the 6 day rotation they would be pitching again next Thursday, Friday, and Saturday. Pitchers usually don’t like to go too long in between appearances, so the Brewers might want them to start on schedule, even if it’s only to go 3-4 innings. That would set them up to pitch with 4 days rest on Tuesday, Wednesday, and Thursday.