If he lived longer

Doubtful....

If I could choose one musician to go back and save from dying he would be the one. He would have had such an amazing life.

I haven't revisited his biography in some time, but I think his health and life were going downhill pretty rapidly by the time LA Woman came out. A lot of weight gain, grew a beard likely to hide a double chin and a broadening face. If you listen close to his singing on that last album, some of the performances seem more like hollering than singing (although maybe that's what the material called for).
Idk, I think Morrison, more than Joplin or Hendrix, (but similar to Brian Jones), pretty much did himself in. He just must not have cared enough for his mind and body to straighten out. He may have been afraid his Muse would leave him and he'd be left an empty shell of a person.

During the production of their last album, LA Woman, he resigned from the doors. Jim wanted to be a writer/poet. As far as I know there was no talk of music or movies. He moved to Paris Before they even Finished mixing the album. He recorded his vocals for LA Woman then told the band he was moving and they could finish the album without him.

I think he would have written some more poetry books and some short stories. Given time to change, grow up and reflect as a person, maybe even an autobiography, but I doubt it. Side note, his poetry books are a good read. Anyhow, I could see him writing a script to a movie, but not necessarily be involved with making it. He could tell interesting stories and created great visuals within his poems and his solo time in the recording studio showed he had an ambition to do something more with his words not only with music.

Perhaps he would have dabled in the recording studios with a few musicians here and there, doing more spoken word pieces with musical interludes and sound effects. I say this because of the "lost Paris tapes" (read this for more context https://en.m.wikipedia.org/wiki/The_Lost_Paris_Tapes ), that resurfaced and also the album "an American prayer".

I think he'd have died young anyway, a bit later than he actually did.

Self-destructive habits are self-destructive habits.

He'd probably be like most musicians who manage to survive. A steady decline in music quality, but continue to release sub-par albums. Tour a lot for the payday, and stick mostly to your classic hits. Break-up with the band a few times and replace various members, then maybe get back together again to boost concert sales. Very few bands have escaped this fate, I don't see why the Doors would be any different.

From what I've read about his existence in Paris with Pam Courson is that he was abusing heroin with her and that it probably led to his heart-failure and death. I can't imagine him living much longer had he not overdosed but if he did and died a year or two later he wouldn't be in the "27 Club" and thus his iconic stature would not be as alluring.

If he lived I think he was done musically. I've seen countless interviews with Ray Manzarek who said Morrison's voice was shot and that he had NOTHING left. Yes, he would have tried to tour again but it would have been a Whitney Houstonish diasaster tour.

One very enlightening story I've heard from Alice Cooper..Alice said he, along with ALMOST EVERYBODY ELSE WHO KNEW JIM MORRISON..was very surprised he made it to age 27.