Well as I understand it Leo had a keen interest in propping up the western roman empire as much as possible. So I'd say you'd continue to see strong ERE support for Anthemius's regime at least until the death of Leo in 474.I'm with those who see the latest possible recovery as being the 460s, but I think Anthemius, a capable Eastern career soldier with the wholehearted backing of Constantinople, could have pulled it off.
LSC is of course right that Germanic infiltration is very far gone by this point, and you're never going to get back to even the situation of the 420s, let alone the days of Valentinian I. The continued survival of the WRE depends on the Emperor and the imperial court remaining relevant to the landowners who after 470 or so quickly came to terms with the new order. In a world where things go right in 468, this process of Roman landowners accepting the new military force in the land, I suspect, happen considerably more slowly.
I wonder also, in the absence of a dynamic Sasanian Iran in the period, and the success of the 468 expedition, how much further support Constantinople would provide for an Anthemius-led regime.
By Majorian, things already went too far : the emperor managed to play Barbarians against other Barbarians (as foederati, particularily), but it was an expedient. Ricimer already had too much control on imperium, and wouldn't accept a too powerful emperor.
Don't get me wrong, a more or less powerful patrician Italy could make the WRE living longer, but would wear it eventually and make it unable to undergo important reforms (as Majorian's demise points). At best the ERE would intervene to make it works again, meaning eventually a fusion of whatever remains of WRE with its eastern counterpart.
Even if he took back part of Africa, I'd tend to think it would be short-lived, and that it would have overstretched its political and ressources possibilities.
As for Aetius, the guy was skilled, but as Majorian, had to resort on Barbarians and eventually had to allow the rise of some of these in order to make things work. Having him survive wouldn't really change things, at least on the big Roman issues.
Africa, the only WRE province untouched by war, and therefore having important enough fiscal revenues, was already lost; and Barbarians were established as foederati a bit everywhere. That made a survival of WRE as an independent entity a bit perillous, as doable as with Majorian (as in not really plausible on long-term).
That said his survival, with a surviving Theodosian dynasty in the West may help things, would it be only because you'd get rid of the political instability its disappearance provoked. Would this be enough for WRE to survive? It's going to be really hard, but it's IMO the latest possible PoD.
I'm not sure what you're talking about : I, in the post you quoted, explicitely pointed that Theodosian survival would have at least prevented the huge political unstability of the Last Emperors, where even people like Majorian had to deal with too much things.I dunno about that, by that logic
I think Majorian could have pulled it off. His demise was inextricably linked to his failure to retake Africa. Given that the Vandals were of the opinion they had no shot to hold him off, I see a significantly brighter future for the WRE if he succeeds.