Lady Russell thought of Wentworth as dangerously impetuous, but it doesn't mean that we should. The fact that he is still alive testifies to the fact that he was smart in his profession. And I cannot agree that CW was not thinking about the future. The text indicates that he pondered a lot on the subject. And besides, he is far too attentive to people surrounding him, and depending on him, to be a 'live for today' type. CW is dependable -- his key characteristic. I think that this particular action is an instance not of rash behavior, but of doing the right thing which no one else has a heart to do. And here lies yet another similarity between him and Anne.