Don't you suppose that the accident flight crew did not have a Plan B? Plan A probably was to arrive in a critically low fuel state, get cleared for a straight-in approach, and land with just enough fuel to taxi to the stand on two engines. Sorted!
My guess is that Plan A was to attempt the flight non-stop, and "re-evaluate" the situation (fuel, weather, delays) as they passed overhead the alternate. This is perhaps how the deal was "sold" to the co-pilot.
It will be interesting to learn what was discussed as they reached this critical point, and how much fuel was remaining. Clearly though the Captain thought there was enough. Judging by his actions he must of thought he had more than enough, or otherwise why would he have accepted a hold rather than simply make a direct to the threshold?
For sure there's gonna be a lot of human factors explained in the report. One can only guess at this stage but mine is that the Captain thought there was enough - maybe "only just enough" - as he passed his alternate. Having "convinced" his crew that to continue was okay, he kept a brave face because he didn't want to look stupid - even though he must have seen that the situation was turning dire.
The bit I simply can't get my head around is why he didn't head direct for the RW as soon as he announced the "electric problems" which surely MUST have been the result of loss of gen due to fuel starvation on one side.