Up to the very moment, we can only speculate what was happening on MH370. Terrorist attack: possible. Bomb: might be. Electronic malfunction: possible. Structural failure is also a possibility.
With regard to "Mayday" call, it shows a possibility that the fatal disaster happened very sudden or the crew were busy to rectify the problem that occurred that night and forgot to do communication.
It might not related to the current incident, 9M-MRO experienced an on-ground collision with A340 China Eastern in Pudong that caused the substantial damage on its wingtip, as recorded on:
Anyone works for Boeing in this forum? Please let me ask you a question:
How much G-Force is needed to activate the emergency locator beacon signal (ELT)?