It is a fact. On the 2nd wave of the strike 747 were taking off by T1 gates. That was not a BASSA rumour, that was reported on tv bu BBC and I was there and I did see a couple of 747 taking off from there. Cant say i they were going around but they were empty.
No they weren't, the holds were full of cargo - the revenue from which alone would justify operating the flight commercially in most cases. But in addition to that, these "empty" aircraft flew to their scheduled destinations from where they operated back to LHR with passengers (and more cargo).