I feel like if a fighter gets knocked out or suffered a hell of a beating they should stay away from any contact training for at least a year.
Ik it's pretty much impossible for the sport and it will suck bad for us, fans.
But I do really worry about their lives.
I'm no doctor though, so, what's your opinion in this subject?
I think it's important to make a distinction between CTE and concussions / TBIs. When a fighter gets knocked out or gets rocked, this is more suggestive of a concussion. Undoubtably, this contributes to CTE, however the "Return to Play" guidelines would probably be your best bet on when to return to training. It generally proceeds stepwise in the following order. To proceed to the next step you must be asymptomatic, while becoming symptomatic puts you back a step.
1 - Rest and daily activities
2 - Light aerobic exercise
3 - Sport specific exercise with no head contact (running, skating, etc.)
4 - Non contact drills with resistance training (hitting pads, hitting the bag, drilling BJJ moves)
5 - Full contact practice
6 - Return to competition
To comment on how long you should wait depends entirely on the person and severity of the injury. For someone with their first mild concussion, 2 weeks might be appropriate. For a professional fighter whose had multiple concussions, it should probably be on the order of 6 months. Generally fighters too short breaks between fights, which means their breaks between training camps is even shorter. Recently, Frankie Edgar comes to mind...
With respect to CTE, the number of professional bouts (typically more than 20) appears to be more important than the number of "knockouts". This is basically because it is sub-concussive blows doing the accumulative damage. For example, I wouldn't be surprised at someone like GSP, whose only had one KO loss and relatively few knockdowns but logged a lot of octagon time, to have CTE later on.
Hope this is helpful.