I was tracking these runaway stars for a SF story i had in mind, but this is the closest one i have heard of yet, and the ArXiv paper describes one that also passed thru 2.5 mya.
Gliese 710 will pass the Sun even closer
Close approach parameters recalculated based on the first Gaia data release
http://www.aanda.org/articles/aa/abs/2016/11/aa29835-16/aa29835-16.html
Close encounters of the stellar kind
https://arxiv.org/abs/1412.3648
tl:dr article
http://www.businessinsider.com/star-hurting-towards-solar-system-2016-12\
"Gliese 710 is about half the size of our sun, and it is set to reach Earth in 1.35 million years, according to a paper published in the journal Astronomy & Astrophysics in November.
And when it arrives, the star could end up a mere 77 light-days away from Earth — one light-day being the equivalent of how far light travels in one day, which is about 26 billion kilometers, the researchers worked out.
As far as we know, Gliese 710 isn't set to collide directly with Earth, but it wil be passing through the Oort Cloud, a shell of trillions of icy objects at the furthest reaches of our solar system. "
Seems like a great opportunity to send out some interstellar probes. The star will be trailing lots of ISM, free gas that would help bring a ramjet up to speed, and track till you could curve towards another destination. Likewise, a solar sail probe launched out in front of it by laser could "hitchhike" , and get some deep space ISM , and EM measurements.
Can we think of some other opportunities that this might present ? If we are past the filter by then, then we will already prob have samples of the Oort objects, but looks like they will be delivering then...
I think they use the models of disruption used by the gas giant displacement/movement.
And it appears it is pretty easy to wobble the system, they are saying that the Planet 9 is responsible for the offset of the solar rotation angle, and the disk of the planets (6 degree).
Solar Obliquity Induced by Planet Nine
https://arxiv.org/abs/1607.03963
There are also a LOT of theories that show that just crossing the plane of the galaxy is enough to disturb the Oort, though the last paper i saw on Neptune doing it was a solid not.
and as an aside, i think the biggest factor of this paper, is that it gives you a hard date for a filter.
Most AP/Cosmologists say we have 4-5 gy ahead , because of solar lifetime, this shortens that horizon considerably. Tough to survive as a planet based society if you have 1-10 my of bombardment by large impactors, 1st one causes nuke winter, 2nd one, heat can't escape because of dust blanket, you end up Venusian...
As the t-shirt says, Dino asks you how your space program is doing....