Ok. Here's the thing... The Universe is so large that you have to assume that there is life beyond our Earth. However, it is quite likely that 'they' are so far away that:
- our civilization will end before we ever make contact with them (i.e. trapped on Earth as the Sun turns into a Red Giant)
- our species will die out, or be usurped by another predator/virus (i.e. we prove not to be the "fittest" and fall foul of Natural Selection)
- one of the above happens to the civilization/species we were about to encounter (i.e. the best we might expect is Archaeological remains)
- the aliens may have evolved from such strange initial conditions that we may not recognize them as alive (i.e. they seem like rocks, or gas)
- or... it takes so damn long for us to make contact that we evolve/transform ourselves out of all recognition...
...the significance of this last option is that if we were to meet our future transformed selves we would regard them as alien, so in other words "us meeting aliens" may be something of a moot point, because we will have become alienated from our current selves.