My perspective on it is that each of us is multi-dimensional and has multiple simultaneous co-existing incarnations that all exist now since "now" is all there is. "Time" does not exist outside of you -- you are All That Is, so time exists inside of you: you are not subject to time, time is subject to you -- otherwise you would not be eternal. What we from our linear perspective call "past" and "future" are just experiences, "points-of-view", because we in this reality experience things in a linear fashion. So yes, from a linear perspective we would label those other incarnations as "past lives" and "future lives", but since everything exists right now those other incarnations already exist right now as well (literally).
There are an infinite number of parallel realities and other versions of you (and other versions me and everything else in Creation). That includes an infinite number of parallel Earths where every "version" of you on each of those Earths believes he is the only version and that the reality he is experiencing is "real". Each one of them experiences birth, life, and death, but each of them is eternal, infinite, and indestructible just as everything is in existence. Each one has its own path, its own memories, and its own experiences. Each is equally valid as any other.
I really liked Bashar's take on this -- if you're interested, search for "Bashar reincarnation and reappearance" on youtube.