It is highly probable that neither QZ8501, nor AF447 for that matter, would have crashed if they had taken steps to avoid the thunderstorm cells on their chosen routes. In both cases, and before they took off, they must have been aware of the severe storm cells they were likely to encounter en-route. Creating a flight plan which avoids an aircraft entering a hazardous situation should be the crew's/airline's first priority. Introducing an exception clause to aircraft insurance policies that would invalidate hull cover should an airline/crew fail to take reasonable steps to stay clear of thunderstorms, might be a first step. It might force a more cautious approach at the flight planning stage on routes where severe weather can be expected. Also, to ensure their actions would be (in hindsight) considered "reasonable", crews might feel more ready to undertake costly detours or diversions to avoid dangerous weather systems.
Avoiding getting into a hazardous situations trumps flight deck heroics every time! Even my car insurance stipulates my cover will be invalidated if I fail to take reasonable care to avoid hazardous situations.