Nope. If the engine is well-maintained and healthy, and has timely change of engine oil + oil filter, then even if odometer reading is more than 3 lac Kms and there is no oil consumption / smoke / weak ring-pistons, etc., there is no need to switch to thicker oil.
That's Good! However, in case of Total Quartz 9000 Future series 5w-30 or any other well-reputed oil and brand, which is fully synthetic and based on latest standards / specs, I think, it will be some sort of unnecessary waste of resources and money, as the oils can easily last at least 5,000 Kms, and do not require oil change at 3,000 Kms (unless / otherwise, severe driving conditions are involved). In case of semi-synthetic and mineral oils, change interval is less, as oil tend to deteriorate early in comparison to fully synthetic engine oils.
Nope. It may happen in case of weak engines IMHO.