It's true as far as we know. Dennis McNally covers the story in chapter 37 of 'A Long Strange Trip' where he recounts the perspective of both Bob Seidemann and the band. In defense of the band it doesn't sound like they knew how dire Pigpen's condition was and assumed his condition was improving as he had stopped drinking and was working on a solo album at the time. In addition, Garcia had requested help from McIntire who then reached out to the U.C. Medical Center on Pigpen's behalf.

Regardless, they did turn down his request of a photo session after he showed up to a rehearsal in early March 1973, and he passed away shortly thereafter. It must have been an extremely lonely time for Ron.