Apparently, one of the group was on a Saudi "dangerous persons" list and was arrested at the airport. So it would seem that they were about to do this when they were caught.
How successful they would have been is another issue; SV
has armed guards on its flights and a series of sharp manoeuvres by the flight crew would have helped to knock them off their feet. The point is, even if they had attempted something like this, they would more than likely have failed. People know that in a hijack situation, the hijacker is now more likely to want to kill everyone, so they will be resisted.
Incidentally, the route apparently targeted was Khartoum, to which SV
As for the three people involved, they may find themselves in a village square after prayers some Friday soon, for a haircut. "Something off the shoulder, sir?"