There could be. A large meteor could strike. A virus or illness could wipe most if not all of us out. A world war could happen. We could use up all of our resources. In terms of threat, I don’t see any immediate evidence to suggest that one of these has a greater possibility of happening than another.
No – at least not on short timescales (the next few centuries): humans have the capacity to make the Earth uninhabitable whether by accident, or design. The major threats to the Earth from internal processes (a very large supervolcanic eruption?) or from external factors (a large asteroid impact) are both low probability but high consequence events – and these pose a significant threat to Earth only over longer timescales.