Mr Good Cat,
Sadly there are many 'black hole' areas where you will get the 'Datalink unavailable' EICAS on both SATCOM datalink and VHF datalink.
Temporary ACARS datalink losses are very common, across Siberia/Mongolia you can lose it for 10-15 minutes.
This is a very confusing loss, much like the AF loss. Once the aircraft has been located then I'm sure there will be a lot to learn.
As to smoking/visitors in the flight deck that is very much up to the airline and the operating authority. In my airline it is forbidden to have visitors in flight and to smoke. On many other airlines those restrictions do not exist. Do you know, specifically the SOP's for Malaysian Airlines? I don't.