lol we have all these scenarios and stories, as people with experience in whatever various fields we have, but the reality most of the time, is these dudes are desperate, unsophisticated, violent criminals, we love to think they are controlled, disciplined, loner types like De Niro in 'Heat', or Affleck in 'The Town'..
anyway, as far as leaving right away, leave the city in a cab, or car service, and I doubt they would check flight manifests and that for a robbery, even one of the this magnitude, unless they had a suspect already in mind...its a city of how many millions? If they are going to close in on you, better with you afar, then close. People leave the city everyday, and never come back. It's a solid plan, staying for a while, but the risk comes with what to do with the money, and the moves you have to make as a result, not nearly as dramatic, but think like 'A Simple Plan'....best bet is to have the infrastructure already for when the job is done, and just execute the plan accordingly. Have a contact in Mexico to set up a bak account, have a contact on houses too, have a plan to cross all the money...but real life rarely works like that, this dude may get caught in a week or two, 2 miles from the robbery with 450k in his house....