Well, there's a metro station close to the stadium (within considerable walking distance.) I've taken the metro after concerts a few times, but the metro closes at 12, so it should be safe to assume that you can make it to the metro after the concert, but of course, if for some reason they start later than usual and the schedule gets delayed, then it's going to be a bit more challenging and pressing to make it on time (given that you have to walk out of the venue, slowly like you do after a Stadium event where there's thousand of people also heading to the exits, and then to the metro.) So, obviously I can't assure you that the metro will be a sure option. Another thing to consider is that the stadium is beside a large avenue (Churubusco Avenue) and right on the other side of the avenue, there is an arena (Palacio de los Deportes) and on the very same day, Pet Shop Boys will be playing at Palacio de los Deportes, so of course everyone is expeting a lot of traffic and the metro will probably be very packed, so that's definitely something to consider. If I were you, I'd take an Uber becuase the taxis going around the stadium and the arena always try to charge high prices given that people are more hard pressed to just find a ride home, so they try to take advantage of it and charge way more than the normal fare.
I'm assuming that you bought the ticket through Ticketmaster? If you did, then you can go to any Ticketmaster counter and you can pick up your tickets there. There are several spread throughout the city, and they're always inside certain departamental stores, book shops, music stores, certain supermarkets and other businesses. I don't know where you're staying, but I'd find one close to your hotel. And they ask for the order number, your official ID and the card that you used to buy the tickets. But yes, you should also be able to pick them at the venue, but I'm not sure where that is. Most times, the Foro Sol ticket offices aren't in Foro Sol, but at Palacio de los Deporters (the arena at the other side of Churubusco avenue) so you probably need to go there. Having said that, one time I went to a festival at Foro Sol, I didn't have tickets but there were still available the very same day of the event, so I went straight to Palacio de los Deportes, only for them to tell me that the ticket offices for that event were being handled at Foro Sol. Did you get instructions as to where you can get your tickets? Maybe it does specify which ticket offices (Palacio de los Deportes or Foro Sol) you should go to.