[Bajoran Rogue]

I saw it, and thought it was good, but one thing confuses me about the Doctor being the last of the Timelords, do they all travel through time? If so, how could they be wiped out, with all that timetraveling wouldn't they find out that something would threaten their existance? Regardless of how they would be wiped out, that makes it seem a bit wierd to me as them being wiped out should be impossible as they could find out before hand and prevent it from happening.