What do you mean by 'we have' 4-5 billion years? A lot happens in that time. Theres a several percent chance of destructive orbital dynamical chaos in the inner solar system during that timeframe coming from the eccentricity of Mars or Mercury, the Earth will almost certainly pop into Venus mode from the increasing solar luminosity by 1.2 gigayears from now (if some parameters are overly harsh maybe as little as 300 megayears and DEFINITELY by 2 gigayears from now). And amusingly enough if we have a longer period of time before popping into the runaway greenhouse, there is a reasonable chance of a carbon crisis in which atmospheric carbon falls low enough that it becomes the limiting factor in biomass production due to the slowing geosphere and increasing burial of carbonate rock. And the average mammalian genus lasts what, ten, twenty million years?

This being said, I again point out that events like this have almost certainly happened many times over the history of the solar system. Even if events like this are rarer than every few tens of megayears due to the larger than average mass of this star, the sun was only 1% dimmer a hundred million years ago. Runaway greenhouses aren't THAT easy to get going and I believe there is evidence from the KT impact that the atmosphere was only strongly disturbed for a short time, potentially single digit years. And there are large impacts not associated with mass extinctions, leading some paleontologists to suggest that they only are associated with mass extinctions when the biosphere was already strongly stressed by something chronic like a large flood basalt eruption. (I myself am partial to the idea that the KT event in particular represents an ongoing low-level flood basalt eruption that got kicked into high gear for a few thousad years by the more or less worldwide 9-pointer earthquake the impact would've generated, providing a double punch). The biosphere and complex life in general is not threatened by impacts.