Just depends what you mean as humans?
We evolve over time - we are nothing like our ancestors from millions of years back and if we are still going in a few million more years - those 'humans' will be nothing like us.
Clearly we can't go on breeding at the rate we have been doing, whilst at the same time depleting the planets resources - as that is simply not a sustainable scenario.
We don't have the technology to get to the next star and until we do we could end up becoming extinct through natural disasters - such as a bloody big comet hitting us, or something similarly as nasty.
I guess though our biggest threat is ourselves, we'll probably blow each other up one day - but I will probably be long gone before then.