A Scammell flag prize on its way Andy! (if I can find the artwork)
Yes, as soon as the jib is off the bank, any sudden movement of the carriage could cause the superstructure to swing (slowly at first but then very rapidly) around 180 deg., given the steep angle at which the machine is sitting. It is only a risk, but a very real one given the effect of the counterweight at that angle.
There is no evidence on the video before recovery begins that the bucket is stuck, or would remain stuck, or has anything in it at all, so no evidence that it would be enough to anchor the jib should it start to spin around. For all we know the dragline could have simply slipped down the bank while moving.
We have no idea if the dragline operator was able to engage the cab lock (locks the superstructure to the undercarriage to prevent rotation for tansport), nor if it was even in working order.
In fact I suggest it is not possible to glean enough information of the surroundings or the circumstances from the video to even begin to question the methods of the recovery operator.
Perhaps this is why it is impossible to answer your question Mike - surely all we can say is that "the BEST WAY is whatever way in which that particular experienced recovery operator chooses to do the job, having first assessed the situation on site."
It certainly looked a very professional job to my untrained eyes. I guess you had to be there, like Ernie (Arthur's mate).