Swissair 111 had an undetected fire on board which was initially underestimated. When the fire was detected, by following the checklist, and the pilots did exactly follow the procedure, they were finally unable to control the aircraft and died.
I strongly suggest to listen to the ATC/Cockpit voice recordings. They pilots decided, due to the smell of smoke which was not found, to head to Halifax. But they had to dump fuel. By that time, they did not know how catastrophic the fire was under the hood.
Remember that the MD11 was not having all the sophisticated systems as a B777.
MH370 had a small little SATCOM antenna on the side of the aircraft. The ACARS system is connected to two redundant SafetyBuses systems which have a 28V battery powered, aircraft independant power source. Generators, Bat or RAT are not needed to have the system alive.
There is no CB in the cockpit, like in a Boeing 737. You cannot pull it out just like this.
So, for me ot logical what event would stop ACARS to send information, except a big booom, like with TWA800.