I would have been (past conditional) happy if he had come (past perfect).
James wondered absently how different his life might have been had he found his way to such a place when his mother had died, rather than ending up in the …
James wondered absently how different his life might have been if he had found his way to such a place when his mother had died, rather than ending up in the …
You have come across an alternate way of structuring an "if" clause - a way in which the "if" is missing! The sense of the "if" is carried by the inversion of word order. "were" and "had" are the words which are moved to the front in these constructions.
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