I don't have any insight on model specific features. My NW2 has metal gears and plastic side frames, but those features are likely to vary by model.
As for the LionChief Plus line in general:
4. Does the remote/conventional switch mean that if the command electronics go bad they can be isolated by the switch so that the engine will still run in conventional?
The short answer is maybe, but not likely. It would depend what exactly broke in the electronics, but even in "conventional' mode, these engines still use their microprocessor. I would have to take a guess that that is why the switch is labeled 'transformer' and not 'conventional'. It's not really conventional control, but a rather interesting, for electronics nerds anyway, system that's in place. So, the long answer, if any of the things that are likely to actually fail in the electronics do fail, the engine will be dead. On the plus side, anyone with a passing, hobbyist level knowledge in electronics can repair any of the likely electronics failures even if Lionel decided not to repair it for some reason.
5. How have the remotes held up?
I've heard stories of remotes being broken. I've never seen one in person, or a photo of a broken remote posted. The remotes shipped with the LC+ engines are made of a sturdy plastic and the weakest point is the speed control knob. that is a standard potentiometer, and as such could be broken by someone forcing it past it's stop, just like the volume knob on any piece of electronic kit made in the last 100 years with a potentiometer.
The remotes that ship with the very low end LionChief engines are a bit more flimsy looking, but I don't have enough experience with them to know if they actually are any worse, or more likely to be damaged.
Lastly, The Universal remote follows the same basic design as the LC+ remotes, but it doesn't feel like as good of a quality plastic. This has no scientific basis, but the orange, glossy plastic seems thin and more likely to crack than the textured blue plastic of the other remotes. It may just be a perception I have and for all I know it could be exactly the same material, but it just feels cheaper. I also don't like that you can see the LED lights glowing through the plastic.
I have a silly question....I run TMCC and Legacy...
Can you operate the Lionchief Plus loco's with the Cab1, Cab1L or Legacy remote in conventional mode?
I run some of my MPC with the Cab1.
Yes, if switched to conventional mode, they will work just like any other conventional locomotive when run under a powermaster or similar device. Keep in mind that you do lose the ability to use the electro couplers when run in conventional. There may be some other features that don't work, as well, but movement, whistle/bell/announcements should be accessible on a track powered with a Powermaster or similar device.