If the transforming union with Christ will not obliterate us, but only make us more of who we truly are, that transformation will only remove what is not truly us to begin with. We have no reason to fear losing ourselves. We need to understand that we will only be losing anything that wasn’t worth keeping. Namely, our selfishness.
This also has implications for dealing with others: we need to see those things in others that are not Christlike as not being essential parts of that person, but only parts that would be burned away in the fire of union. Ultimately, our true selves are Christ as played through the instrument of each individual soul. And with St. Paul we hope we can say, “It is no longer I who live, but Christ who lives in me.”