There isn't even a Hell anymore or never was? Why did Paul say he would give his soul up to save his brothers?
Regarding Hell, I think we have assumed upon an awful lot of theological history as to why those comments were ever recorded in the first place. I do have numerous posts on the subject.
As to why or upon what understanding Paul made such a statement in Romans, I am not sure, though I think I can safely say that "Hell" doesn't take center stage in his thoughts since he never once mentioned Hell in the letter. It was the estrangement to Christ to which he referred. And I'm not really sure he meant the statement as a kind of trade-off but very possibly as a relational thing.
I remember hearing one brother (many years ago) state that the phrase about wishing himself accursed was just as easily translated "For I used to be wishing...". Though it obviously contradicts the popular consensus on the phrase, and may seem stretched, it wouldn't be the first time that Paul spoke of his own intimate former agreement with those from his Jewish roots ... and that personal realization of their hardness of heart only served to strengthen his own heart ache. I thought I might throw that in for something to consider.
I still think there's a basic fault in the contemporary focus on the "destiny" question as it is so bogged down with a recognition of people (and therefore the "whole world") according to the flesh. I see so much demand in this argument that unless everybody in Adam gets saved then God would somehow be untrue to His own determinations and purposes in Christ. And there's the fly in the ointment, for NOBODY in Adam gets saved ... there is a NEW creation in Christ.