The thread about racial level limits in AD&D made me think of Rifts Juicers. A powerful class that is theoretically limited by a Juicer's severely shortened lifespan.

"Burning out" is a big part of Juicer lore. Those who try to detox before their 5ish year lifespan have mixed results due to being psychologically addicted to being a chemically augmented super soldier.

But this very rarely (as in, never) came up in our Rifts campaigns. Usually we wouldn't run a campaign long enough to deal with a Juicer's "Last Call".

Did anyone ever have a Juicer run till they had to deal with their burnout? If so, how did it play out?

Ran a lot of Rifts games.

Nobody wanted to be a Juicer because of that reason.  So, like you, it never came up. 

Also, Crazies were unpopular as well because of the negatives. 

Then again, half our team were Veritech pilots from RoboTech, the game we started in.  Rifts just became our middle game, and ended in Phase World.  We consider PW to be its own game setting. 

I played in an established Rifts campaign that had an old juicer nearing the end of his life. He tried to detox a couple times, but ended up just Leeroy Jenkinsing it up and committed suicide-by-dragon during an encounter in which we were clearly overmatched. The rest of the party escaped, and he died a hero, so it worked out.

When Juicer Uprising came out, I had moved on to other stuff, so no direct experience with those other types other than reading them and seeing the obvious and obnoxious powercreep that took over Rifts.

I played a Juicer back in the day, but the campaign ended before I got close to the burn out date, so I didn't have to try and detox or chose to go out in style.

Now, I love the idea of Juicer, and made a Juicer type option for my home brew Traveller game (using inspiration from BtB Traveller, Rifts - normal Rifts, and Rifts Manhunter setting, Blade runner and some other games / pop culture). I gave it and one type of synth a limited life span to represent the burn out . However, in the one campaign of the setting I'm running no one chose either of those options. so I don't know how well it will work, or how the player will deal with the 'you are close to your final use by date ... you feel your actual cells starting to rip themselves apart .... '

Savage Rifts actually made the Burn out a real Mechanic. Every Juicer has a burn out score they have to test against at the beginning of each session.

If they fail, the score gets lower.

In the course of play they can also get a boost to their rolls by testing against the Burn out rating. Wagering shortening their life for a quick boost of power.

When the score runs out, it's last call and the Juicer will die during that session.

Juicer Uprising was one of the Rifts books I remember fondly.  One of my first Rifts characters when the core book came out was a Dog Boy Juicer and he was a beast.  He never burnt out, and I am not sure if the game would have lasted long enough for him to do so, but as soon as he had enough credits he converted to a full borg.  The only other Juicer I played was a Dragon Juicer alongside an Undead Slayer and a Godling.  The GM eventually just ran an adventure where I drank ancient dragon blood and became immortal as we were getting into some time skipping on a cosmic level.