No. It wouldn’t be a lager then. Ales I usually don’t let sit on the yeast more than three weeks.
That’s a pretty warm temperature for a lager fermentation. Leaving it on the yeast at that temp for that long will be fine though.
I have never tried that, Tom. I would think at 68F for 8 weeks, autolysis or something else ungood may start, but like I said, I have no experience with storing beer on the primary yeast for that amount of time, so I will take your word for it, probably still wouldn’t do it though. 
A general rule of thumb for primary fermentation is:
Ales: 14 days at 68F
Lagers: 30 days or less at 50F , sometimes a Diacetyl rest will be necessary for several days at 68F
This is also dependent on yeast strain. Some yeast strains are more active than others, and will therefore ferment faster than others. Experience is plus. Knowing how a particular yeast behaves will enable one to anticipate terminal gravity. The main factors to consider are the yeast strain, available oxygen, fermentable sugars and time.
The most important tool for the beginning brewer is the hydrometer. The air-lock is a good indicator, but the hydrometer can tell you when terminal gravity has been met. Once terminal gravity has been met, then the beer can be tranferred.
Let your hydrometer be your guide. 
Autolysis is not as much of a problem as some people think. It may be that the higher quality of yeast we get today makes it less of a concern than when we were brewing with the packet that came under the cap of the extract can
So basically, healthier yeast lives longer.
In a 30+ bbl conical, absolutely. Under a two-foot beer column in a bucket, autolysis just doesn’t seem to be a concern on any reasonable timescale.
Absolutely.
That’s a really good point too, that could be where the autolysis fears come from.
Makes sense to me. Pressure and temperature effects. I’m very familiar with this on non-living materials (HPTGA).
I’ve come to the conclusion that a transfer to secondary can be useful under certain circumstances and when done at the right time. When you are fermenting a fairly big beer in a bucket, you might wind up with some oxidation before the beer is completely finished. Under those circumstances I would transfer the beer to a carboy right as its finishing active fermentation, along with plenty of the yeast cake. Transfer while the liquid is saturated with CO2 minimizes oxidation, and including yeast prevents it from stalling out. The environment of a full carboy with a good stopper and airlock, will introduce less air to the beer as it finishes.
Alternatively, you can ferment in a carboy from the beginning and use a blowoff tube and not need to transfer. I’d still avoid a lot of head space if I was going to keep the beer in the carboy for several weeks.
One thing that I always keep in mind on this debate is santitization. Not all of the tales of off flavors come from the beer sitting on the yeast cake too long, but rather bugs that made it into the beer.
That said, yeast are the only thing that will ‘clean up’ your beer. If that is what you want, then leave the beer in contact with the yeast as long as possible. IMO, the only reason to secondary is to 1) leave a little off flavor, and 2) get clear beer fast. If you want a little yeast by-product, e.g., a touch of diacetyl in an ESB, then transfer to secondary. If you need to turn over your beer faster and want it clear, then transfer to secondary. When you transfer beer, you force the yeast to flocculate and fall out of suspension faster. I believe the theory on this is that the mechanical action of the fluid transfer causes CO2 to offgas, creating bubbles and thereby nucleation sites for yeast to flocc. There are many pics of this online where people do side by side comparisons, and the rate at which the yeast falls out of suspension is dramatic.