Okay, so a couple things here.
1.) We have no idea yet if there is an "Ark" or whatever.
2.) Even if there is one we have no idea when it was built.
There are so many things we just don't know (assuming the leak is true) that I think it pointless to get too worked up about it. However, to help assuage the fears of those who think that any trip to Andromeda would be impossible, I present two scenarios for traveling to Andromeda.
1.) Sleeper ship/s. Assuming that there is some way of discharging on the way (possible given updated technology and solar systems which actually exist between Andromeda and the Milky Way), and assuming proper sleeper pods were maintained, the trip would take around 230 years or so at 30/ly a day (standard speed for Council ships.) Necessity is the mother of invention, and we know that the Asari councilor began seeing to "continuity of civilization plans" after the Fall of Thessia.
2.) Worm hole/Remnant portal etc. Another possibility is that another species at some point in the previous millions of years of cycles decided to flee the Milky Way and left their means of retreat behind. This could be a fun scenario because it would allow for some connection to the Milky Way's past.
So basically we could some combination of Mass Effect, Voyager, Battlestar Galactica, and/or Stargate: Atlantis. If that combo doesn't excite you then I don't know what will!
EDIT: Oh and throw in a bit of Andromeda + Deep Space 9 in there for fun. The possibilities are endless!