Let's be extremely clear, there is no chance that Berlinguer might try to create a People's Democracy.
He was still deep rooted in Communist ideals, but he was at huge distance from Moscow.
Probably, after Afghanistan, if he survived, he would take a stance similar to that of the Socialist People's Party in Denmark, left-wing non socialdemocratic radicalism.
It then depends on who gets the upper hand in the Party after the inevitable split with Soviets die hards, and what happens between the socialists at the same time.
If the Amendolian right wins, they will move towards socialdemocracy, but with friendly relations with the Eastern Bloc, ala Brandt.
Berlinguerians will grow more and more anti-Soviet, to buy legitimacy, maybe increasing cooperation with Yugoslavia and Deng China before Tien An Men. Then, it depends again: if the Ingrao radical wing prevails, they will become Linke-esque after the fall of the Berlin Wall. If the Berlinguerian centre prevails again, they will move towards socialdemocracy, and probably embrace neoliberalism even more enthusiastically than in OTL.
The Socialists, now: if De Martino goes on prevailing, he will eventually lead his Party towards unification with the Commies. Craxi and Lombardi, who at the time were close even though distinct, could create a Eurosocialist party, but with greater Keynesianism and a greater attention towards the extreme left. Paradoxically, they might become the Socialist People's Party of the country, whereas the Communist + leftwing socialists take a Scandinavian path, welfare state and social moderation.
If they defeat De Martino, they will have a similar position to OTL, eventually merge with socialdemocrats and we will have quite similar 80s with regards to leftist struggles for hegemony, but with no Pentapartito coalitions. In the end, centrist Commies and socialdemocrats will eventually merge, as the bad blood of the 80s with no Socialist coalitions with Andreotti will probably decrease after 1989.