it only takes o few seconds to select heading mode and change heading or use a nearest then direct to function, nothing complicated or time consuming.
The auto pilot will happily keep going where it has been told to fly
Which would have been straight over Indonesian airspace and not consistent with ACARS pings, nor radar.
So - it almost certainly didn't happen that way.
I don't think we can say anything almost happened for certain.
I admit that what I think is only a theory. There has been so much contradictory information it's hard to be sure of anything.. While my theory is along way from being proven there is no incontravertable to disprove it either.