Translation:When I die all this will become yours.
GennaroRug indicates above that either present or future will work - but I think present is probably more idiomatic. I mean, it's used in the English phrase as well - "When I died" is present tense, but is understood to mean "When I will die". Seems like a parallel usage.
Interesting that the English and Italian dual definitions of "to become" are the same. In one definition, some thing is transformed into something else, as "Wood becomes ashes when it burns" - but "This will become yours" is different from that kind of transformation - the thing itself doesn't change at all, just the ownership of it. So, in Italian and English, "this will become yours" is understood to mean "The ownership of this will become yours."