yeah people do that, a friend of mine moved from Mexico to the usa and before doing so maxed out every credit card they had with mexican banks, and it hasnt backfired yet tho its only been 2 years since he migrated theres still time for it to come back and bite him.
While you are in a foreign country, the collection agency can only sue you by going through a foreign court. Unless you owe an exceptionally large amount of debt(my guess is in the millions), it's unlikely that the collection agency will be willing to pay the costly fees associated with suing you out of the United States.