Cracked rubber is not likely to cause you to lose control of your vehicle. There might be a once in a blue moon chance that dry rotted rubber could disentegrate suddenly and the car could have some bad handling habits which could then lead to a wreck. This is really grasping though.
Some dry rot cracking in aged rubber is normal and in a case like a lower control arm bushing I really would not worry about it. If the bushing is bad enough to worry about there will be some slop in the lower control arm.
If you ever did need bushings, here you go.
The quote of 1200 is pretty high and this job could be done by an independent shop for far less if needed. In the dealer's situation they would be using a genuine Toyota lower control arm with the bushing already installed. It is very likely that the dealer cannot order a bushing only from Toyota. They must buy it as an assembly.
This kind of thing is nothing new; all car makers do this. It is an aggravation to have to buy 90% extra to get the 10% needed but most of the time the dealer's hands are tied.
JMHO, but I don't think the dealer was trying to deliberately rip you off. It's possible that the tech doing the oil change is a relatively inexperienced guy and he may honestly believe the bushing is horribly bad because of the cracking.
He relates this to a service writer (most of whom are not mechanically inclined) and there you are.