1st issue: Hard to say without personally looking at it. Balance shaft bearing failure can be just as catastrophic as any other bearing failure.
2nd issue: Your mechanic is an idiot, it is not common for that to happen if you maintain it well. I would suggest you get a new mechanic.
1st issue: Hmmmmmm, not good news
2nd issue: Mechanic is not an idiot, as that's exactly what he said - if it's had a good service history, esp scheduled oil changes, it will be unlikely to blow anytime soon (esp as it only has 102,000 on the clock).....but the service history on the car is unknown (had 92,000 on it when bought). Plugging the oil gallery and removing the balance shafts without balancing the engine is a foolish move. He has filled your head with poor information, that could possibly end in tears, but hey, if you think he's not an idiot, then so be it.
Have a nice day.