Funnily enough, the answer to this question is preoccupying scientists as I write.
Particle theory and quantum theory seem to point out that everything is made from the same particles/energy. And it has been an axiom for generations that matter cannot be destroyed, merely changed.
So this would suggest that "we" are around for ever, in one form or another and ultimately in everything.
Also, perhaps more interestingly, if we accept that time has no limits and this mass of energy/mass is indeed around infinitely, then what you and I are today will be endlessly repeated..and also means copies without limit of "us" - and every other life-form and object ever evolved in the universe - exist simillarly in other time dimensions and perhaps other planets and stars.
This would mean we are, indeed, everything, and everything is, indeed, us.
It's a hard concept to grasp and what it means also, in effect, is that reincarnation is a fact.