Translation:Who knows what I would have become without him?
'Who knows what would have become of me' is a far more natural translation than the one given.
when "lui" is before the verb, it can be used fr both male and female: "je lui ai demande" = I asked him/ I asked her
When it is after the verbe it is male only: "je demande ma route sans lui" = I ask for directions without him. "je demande ma route sans elle" = I ask for directions without her.
In French, we make the distinction when the "lui" is the recipient of the action (called COI or complement d'objet indirect) and when it is used for something different.
I asked Helen (whom) for directions (what) = I asked her for directions = Je lui (whom/COI) ai demande ma route (what/COD) = J'ai demande ma route a Helen the "a Helen" is the COI, the recipient of the action...
"Devenu" should have been accepted. We can't tell if the person speaking is a female or a male.
Remember that the passé composé uses avoir in conjugation most of the time (as in "il a eu" or "vous avez dit") but some words (like devenir) use "être" - so "je suis devenu quelque chose" or "je serais devenu un avocat". That's all that's going on here