As the coolant gets lower and lower things will progress as follows:
There won't be coolant in the coolant expansion tank even when the engine is warm.
There will often be insufficient fluid to circulate coolant through the heater core and the heat won't work. A water cooled throttle EGR / body could suffer too.
The water pump will pump most of the water ...
there are several ways that rings are lubricated for example in a two stroke its done by means of petrol /oil mix in certain 4 stroke engines you will find a jet which sprays oil onto the bore and skirt of piston and as stated the oil scraper rings do not remove all oil also the cross hatch in the cyl holds a degree of oil which provides some lubrication