The Scarlett breakup (2010) started the decline, the Lupa drama (2011) sent him flying downhill, and the movie announcement (2014) finished him.
The early years of the decade were a dogpile of roadblocks and worsening mental illness he has never recovered from. His downward spiral can be measured in the decreased amount of output between, and following, those three pillars of destruction.
The damage he's done to his mind and body is indeterminable; only a medical professional can answer that. It's clear (via his Twitter career) Noah is too narcissistic/self-indulgent to get help, or even admit he has a problem—the first step to any recovery, substance abuse, depression, PTSD, etc. In Noah's case, the therapist has it out for him, and American health care conspires against the little guy. So our only hope now is a miracle.