So, would it be feasible for Ferdinand Marcos (and his son) to maintain his dictatorship through the 80s and beyond? What would be needed to maintain such a thing?
If Ferdinand Marcos and his heirs want to maintain dictatorship beyond 1986 is to expropriate further the properties of their opponents and their supporters, to the extent that most or all of them would be sent into exile primarily to the United States, and have the entire country be totally populated by his loyalists and apathetic people. Marcos needs an economic stimuli to sustain his dictatorship beyond 2000 like massive oil and gas discoveries in Recto Bank or anywhere in Mindanao like Sulu Sea and Liguasan Marsh. Marcos also needs to let Gerardo Sicat and Cesar Virata running the economic affairs of the country after oil price crash in 1981 and avoid debt default altogether.
The reason on why his Indonesian counterpart, Suharto, stayed in power until 1998 was because of oil revenues which were able to cushion Indonesia's economy during the oil price crash in the 1980s while at the same time, he let his economic advisers run the economic affairs and successfully able to transform Indonesia into an export-driven mixed community-manufacturing economy unlike ours and had Marcos done what Suharto did, we would have been more economically competitive than Indonesia as the former had higher GDP per capita in 1970 over the latter and if we had growth trajectory similar to Indonesia from 1970, our per capita would have been roughly $10,000 today like Malaysia in OTL.
Would Marcos still have enough of a power base to retain control and restore a semblance of order in the Philippines if the EDSA Revolution became violent, or would an earlier PoD be needed?
Marcos cannot anymore and would be unlikely to fire the protesters with bullets and bombs. He was not that stupid to do that, by the way. Marcos in 1986 was already dying and had he won the snap election convincingly, he would stood down from the presidency or die in office by 1989 and let Arturo Tolentino succeed him. The reason on why he restored the position of vice president was to provide an orderly succession in case of his inevitable resignation or death and to save the country from civil war between Imelda and JPE's supporters.
And if such a thing could be achieved, how would it affect the wider world?
The United States government would surely support the surviving Marcos regime, provided that there are semblances of democracy like orderly elections and free press which might be possible under Bongbong or Imee's regimes not Imelda.