Sounds like a case for The Jeremy Kyle Show!
Many years ago, one of my family members was in the police. He said that they hated attending 'domestics' for all the reasons given previously. The usual result is that the couple concerned invariably make up very quickly afterwards, and indeed this appears to have been the case here.
Had tezzer, (and/or someone else) intervened it would almost certainly have resulted in a fracas, given the amount of alcohol and unidentified tablets they had apparently consumed. This in turn would likely have resulted in a diversion to a third country, with all the problems this brings.
EK employs multi-ethnic, multi-cultural cabin crew (perhaps to a greater extent than any other major carrier), and this may have been a factor in their decision not to intervene in this case. Oh, and before anyone kicks off, I see this as a positive in general terms, but when a difficult situation such as this occurs, it may be a disadvantage.
Many years ago, I was at the front end on a domestic flight in the US (ID upgrade), and a similar event took place. The guy sitting next to me was quite concerned, and called a member of the CC. They said they were aware of the problem, but had been instructed not to intervene, unless it endangered other passengers, which it did not.
A very unpleasant experience for tezzer. My flight was 2.5 hours - his was much longer. Oh, and on arrival in MIA, the offending couple walked (or more accurately staggered) down the steps (yes, it was that long ago), hand in hand, towards baggage reclaim.