Roth's Heroes: The Many Guises of the Protagonist in Roth's novels

At the conclusion of Philip Roth's debut novel, "Letting Go," the protagonist is completely isolated - living alone in London, estranged from his father (apparently remarried - Roth, probably sensing that this novel could go on forever, wisely decided to forgo some of the dramatic scenes he was building toward: the re-marriage of Dr. Wallach, the confrontation between the Herzes and the Bigonesses when the Herzes show up - if they ever actually do? - to claim their adopted baby, Rachel), cut off from the Herzes, now presumably happy as young parents (though their loveless, sexless marriage seems deeply troubled), cut off from former girlfriend Martha, who presumably is married or about to be to lawyer Jaffe - none of the characters ends up truly happy, even though the ending is traditionally "comic": marriages, things born and reborn. Roth also leaves one thing strangely ambiguous: our last scene with Wallach has him collapsed on the floor, victim of some kind of stroke or seizure, and I'm not sure how to interpret that. Does he fully recover? Why in the end is he in London and not in Greece or Turkey (he was applying for jobs in those locales)? It's not clear what became of Gabe Wallach, but we do know what will become of him: he will go on to be, in many guises, the protagonist-hero-victim in dozens of other Roth novels, the many other versions of the Jewish-American intellectual hero in crisis and agony (Portnoy, Kepesch, Zuckerman, Roth himself, et al.).