D9009
I believe it is Commanders discretion to do what he / she believes is the safest action for a safe outcome. In an Emergency and if you have a credible Bomb Threat, that would be a Mayday and land at the nearest airport. ATC instructions can be disregarded for a Mayday.
It would not mean making an 180 degree turn, into a country run by a dictator based on ATC instructions alone, to fly to an airport that is more then double the distance of your original destination airport.
But it would mean that you would need be at least slightly clued up on current local world affairs, to know that you really don't want the hassle to divert into a non-EU country, run by a dictator.
If the aircraft was never intercepted before the border of Lithuania by one more MIG's, then serious questions should be asked why the crew diverted to Minsk.
There does not seem to be any passenger statements / confirmations that the aircraft was intercepted by any fighter jets.
Also the "logic" of a bomb threat, why would a country then want to invite this aircraft to land in their own country, while they could leave it Lithuania to deal with it.
If there was MIG on their wing / tail, then that's another story, then I would say they had no other choice. Let's hope there will be a proper report of what really happen.