Like I said, I don't think it will happen, but our civilization will be gone from many causes, the earth is actually more than halfway old, as aomething WILL get us in a billion years or less. Of course, nothing any of us have to worry about in our life times, but here are a few theories:
1. Snowball earth(whole planet will be covered in ice at -40 degrees)
2. Surface to hot as a result of the growing sun
3. Sun starts It's end of lifecycle, as it will grow, then contratct, then grow again, and roast the earth, if this doesnt happen the below will
4. Sun exploding and creating a supernova, therefore positively wiping out all life.