777fly:
Aircraft follows Alt Nav manually entered lat/long waypoints
We wouldn't enter waypoints for know places using manually entered lat/long (difficult to remember), we would enter their codes. eg for Penang we would enter 'wmkp' or 'vpg'. Once the aircraft reached that waypoint if no other waypoints were entered into the FMC, the aircraft would continue on the current inbound heading. ie approx SW towards Madagascar.
Tankengine:
Or: the aircraft was turned in heading select and simply followed that heading till the end
Once again if a heading was selected for Penang / Langkawi the aircraft would continue SW/W towards Africa.
The available tracking data for MH370 does not support either scenario.