747JJ, I do indeed know,really know, where you are coming from with this. 20yrs Capt on 767,no doubt very senior in the company, no doubt mindful of what LOT would like. . . . but, as a previous poster has posted, the same thing in the dark,in the US, would have been a whole lot more difficult for all concerned,it would have been a good idea anyhow to burn off/dump fuel, so time would have been needed before any attempted landing.
I will leave it to those familiar with the 767 to state whether the loss of that system alone would have given them any qualms before setting off over the pond. Outside my type-specific knowledge, so cannot really comment.