I'm not sure exsactly what you are trying to focus on, but I'll tell you what I know. The main problem when these gaskets leak is that the coolant leaks and then ends up in the oil/ crankcase, causing problems. Oil mixed with water and glycol (emulsion)is not good at preventing engine wear and deposits. The word sludge comes to mind, too. The oil's protective additive package is quickly overpowered by the incoming coolant. Sometimes noise such as lifters tapping is the first warning you get. Hydraulic lifters have some very small oil passages that won't flow oil if sludge is blocking the flow. For those of us who actually look under the hood once in a while, we may notice the coolant reservoir is low or empty. This is your cue to at least visually check the oil, and then pull an oil sample to check for coolant or water in the oil. In the case of our friend's 2003 Buick Rendezvous 3.4L, they had a loud lifter tap, that signaled them to have it checked out. Their oil had been changed within last 2000 miles, but had very orange look to it (Dexcool). For some reason, the coolant "low level" light never came on, so they never noticed anything up until that point. At 49K miles they paid a local shop nearly $600 dollars to replace the leaking intake gaskets and flush the engine's oil system. The tech told him that their Buick got the newest gasket revision and it would be interesting to see if the new design would be better than the last several generations of same gaskets.
As far as what else can go wrong, my neighbor's brother had an Olds minivan with the 3.1 or 3.4 engine and he had me come across the road to listen to it. The engine sounded like it was coming apart because it was. We pulled the dipstick and found an emulsion that looked like a chocolate milkshake. I told him to stop driving it immediately unless he wanted to destroy the engine completely. He planned to change the oil, maybe run a flush through it, and then go trade it and dump it on someone else, but never got that far. He instead completely ruined the engine driving home that night. Some guy that eventually bought it from him for $600, told him that the camshaft had broken in half and also had severe bearing wear on the crankshaft as well as piles of sludge throughout. He then bought a used engine and put it in instead of rebuilding the old one. Yes this was an extreme case, but I'm sure many others have done the same thing. This van had only 80k miles on it when this happened.