PWInsider reports that The Undertaker will be appearing on at least one RAW after the SummerSlam pay-per-view, possibly more. They speculation that it will most likely be the RAW directly after the the pay-per-view in Brooklyn, NY.
Speaking of the RAW after SummerSlam, locally advertised is John Cena, Randy Orton & Roman Reigns vs. Seth Rollins, Sheamus and Bray Wyatt.
Source: PWInsider.com