It would be no exaggeration to say that for him, his wife was his very life.
Literal
Him [for-にとって], wife [topic-は] his life itself was [quotative-と] say-[even-ても] never exaggeration not-is.
~にとって ('for him, from his perspective') scopes the emotional claim. 命そのもの ('life itself') uses そのもの for emphasis. ~と言っても決して大げさではない ('it would not be an exaggeration to say') is a set literary pattern for underscore dramatic statements. 決して ('never, by no means') reinforces the negation.