In May 2004, Mueller, a longtime smoker,[citation needed] was diagnosed with esophageal cancer, and a benefit concert was held to help him with his medical bills. In September of that year, Grant Hart and Bob Mould of Hüsker Dü reunited for the first time in 17 years at the Rock for Karl benefit in Minneapolis.[3]Paul Westerberg also made an appearance, as did Soul Asylum, in Mueller's last public performance. Mueller died of cancer in June 2005.[1] Mueller was subsequently cremated and his remains reside at Lakewood Cemetery in Minneapolis. His widow, Mary Beth, resides in Minneapolis. In 2014, she founded the nonprofit Kill Kancer in Karl's memory to help continue the fight against cancer.[4][3]
As of 2020, Mueller is still credited as a member on their Facebook page as a tribute.
Posthumous
In July 2006, Soul Asylum released The Silver Lining, a studio album featuring Mueller's last work.
Mueller was also pictured on the cover of the EP Clam Dip & Other Delights, released on April 14, 1989.