I assume there are no sources that outright "expose" it, but it wouldn't be surprising if they were just protecting the kayfabe.
I can see different reasons gladiator combat could make it into sources, but I doubt anyone was writing with the intent of passing on the idea of how it's done to people who will live after the fall of Rome. In their own day, if the crowds weren't aware of it being fake, then it would be more lucrative to keep the secret, and on the other hand, if they knew, I doubt people were learning about the art of it from the books - people getting into it in any form would be shown the ropes, not read about it. (I suppose dirt sheets and such from the time period would be possible?)
Mainly concerning deaths, I can see why you wouldn't want a great gladiator to die - maybe they just fake died and retired? A guy who's a good draw could later be brought back as a different character or train others - that sounds more financially smart than letting top guys in their prime die.
P.s. I'm not trying to push this as a conspiracy theory ("What the Senate doesn't want you to KNOW about Spartacus!") or anything. It would be cool to get exact sources that would make me go "yep, this theory's dead"
There was typically an element of cooperation in gladiatorial combat (at least in fights between gladiators proper; the same was much less likely in fights between damnati, prisoners sentenced to die fighting each other in the arena). First, there were rules and referees. We don't know the actual rules, but the existence of rules in mentioned in literary sources. The rules possibly excluded certain techniques (e.g., eye gouging). Each pair of gladiators appears to have usually been accompanied by one or two referees (who carried long sticks which could be used to separate the fighters, as commonly used by HEMA referees and SCA marshals today). Fights were (at least sometimes) stopped when a fighter was wounded, and the referee(s) would check the wound and decide whether the fight should continue or not.
Beyond this, an important goal of the fighters was to display courage and skill. This was something the crowd wanted, and could lead to fame and admiration whether the fighter won or lost. Importantly for the fighters chance of survival, a losing gladiator was more likely to be spared if they had the support of the crowd, and more likely to be killed if the crowd was against them. Gladiators didn't need to kill their opponent in order to win - it was sufficient to inflict a wound that either incapacitated the opponent or was at least severe enough to justify surrender. If they were clearly attempting to actually kill their opponent, their opponent would reciprocate, either in self-defence:
Taking his position [Sisennes] fought helmetless and right away he himself is wounded, having been cut behind the knee by a curved sword [His opponent was a thraex.] with the result that much blood flowed. I [Toxaris] was already dying with fear, but [Sisennes] alertly pierced with his sword the chest of his opponent as he was boldly rushing in for the kill. As a result, his opponent fell before his feet and he, in bad shape himself, sat on the corpse and came close to dying himself, but I ran to him, helped him up and comforted him. And when he was dismissed as the winner, I picked him up and carried him back to our quarters.
or because that behaviour was driven by mutual loathing:
If you are interested, I will defeat and kill him, he said. This is the way it will happen: I myself before I receive his sword in my face, will thrust mine in that wretch’s stomach and lungs. I hate the man; I will fight him in a rage, nor will it take longer than for both of us to grasp our swords in our right hand. This is how much I am filled with fervour and hatred of him.
Of course, this kind of talk shouldn't always be taken seriously - some of it could easily be the equivalent of trash-talking opponents in modern pro-wrestling.
One thing affecting this is that a gladiator's opponent often knew him (or her) well, since gladiators usually fought an opponent from their own familia (gladiator troupe/company/stable). A history of killing opponents could easily make one's opponents more likely to kill in order to save themselves.
As already noted, the display of courage and skill could be a matter of life or death for the loser. For the winner, it affected their reputation. Crowds recognised the ability to win without killing as a worthy skill - Martial wrote a poem praising a gladiator named/nicknamed Hermes:
Hermes, trained to win without killing;
(and also praised his out-of-arena prowess: "Hermes, the care and despair of gladiator groupies"). Generally, there were many benefits from fighting to win through wounding rather than killing. This led to a fairly low fatality rate when gladiators who fought well were usually spared: in the 1st century AD, gladiators had about an 80-90% chance of surviving a fight. The winner was less likely to die than the loser - the loser was not always spared, especially if they had fought badly (not displaying courage and skill), and the loser was usually wounded more and/or worse than the winner. Even if the winner didn't intend to kill the loser, accidents could and did happen, and wounds could get infected despite the best intentions of the winner.
This leads to a possible answer as to how often gladiatorial fights might have been "worked" (i.e., have pre-determined outcomes, possibly even being scripted). From the above 80-90% chance of survival, if we assume that the winner almost always survived, the loser would have a 60-80% chance of surviving his loss. If you were a gladiator, would you accept a 20-40% chance of death from taking a loss in a worked fight? While an approximately 1 in 3 chance of death when losing a fight might seem quite high already, things got worse in the 2nd and 3rd centuries, when it became unusual for the loser to be spared (overall, the chance of a surviving a fight fell to a little below 50% (since the winner might die from his wounds), and the chance of the loser surviving was very low). It seems very unlikely that 2nd and 3rd century gladiators would have accepted almost certain death from a scripted loss.
Therefore, while gladiatorial combat was partly cooperative, with the fighters often trying to avoid killing each other, it's unlikely that the fights were scripted or worked.
For further reading, see
(from which the above quotes were re-quoted). See also
where u/XenophonTheAthenian discusses, among other things, the difference between gladiatorial fights and things like arena-executions of damnati.
Mainly concerning deaths, I can see why you wouldn't want a great gladiator to die - maybe they just fake died and retired?
It's difficult to "fake die" when your throat is cut in front of a crowd of spectators.