So if I read things right, you don't need Perron to survive unto 1980, you need Evita to survive him instead of the other way round?
Evita was his second wife and died in 1952. Peron's wife during the 1970s was Maria Estela Martinez, usually known as "Isabel". Eva Peron wasn't in the line of sucession in 1952 and I don't think she'd be able to govern effectively in any case (she wanted to arm the unions, for instance).
I agree with Ruperto: the coup becomes unlikely. There will be some amount of kidnapping and torture - that was the Armed Forces doctrine at the time - but nothing in the scale of the dictatorship: Peron wouldn't consider peronist union leaders as enemies (for obvious reasons) and would have no reason to let torturers keep torturing people for months.
So less deaths, maybe trials for the left-wing terrorists (otoh the military would want to cover up the torture, though). IOTL the dictatorship had, for all practical purposes, defeated the insurgents by 1978. I don't see that "time table" slowing down. If anything, it may even be sped up, as resources are employed to go after actual armed insurgents. I'm going to guess he'd resign once that's done, or nearly done, due his health. Bonus points if he manages to get his wife to resign as VP before that, but he chose her as VP, so that's unlikely.
Diplomatically, Peron was going to accept some sort of joint administration of the Falklands the UK had proposed, so the war gets butterflied away. He should be able to achieve better economic performance (is worse than OTL really an option?) but at some point he's going to hand over the reigns to his wife and VP. I'm going to guess the economy falls, but not as much.