Sadly they could have lost their lives from encountering bad weather, even if they followed all those guidelines.
There are other perils such as the one cited above at the WSJ link I posted, related to how the weather affects jet aircraft engines.
Then there is the peril of weather-related pitot systems failures, as happened to Air France 447.
And one weather trap not mentioned at that link: sometimes the radar signal is attenuated from the thunderstorm cell, hiding the thunderstorm behind it. So the crew avoids one thunderstorm, expecting to turn into a clear area behind it, only to encounter another big cell.
The guidelines that we know have failed on multiple Malaysia flights are those for the ELTs and distress calls.
Troubled aircraft arent being located. That’s a failure of the mandated location systems and standards...a failure of bureaucrats.
There should be resignations and firings.