An expat would want to keep his account in dollars right now even if he moves to Mexico. 
Reasons to retire overseas? 
High quality, broadband Internet service in Portugal costs about €10 (US $11 or £7.50) a month. The country’s aim is for Internet service to be free for everybody by the year 2020. The reason why the Internet connectivity is so cheap in Portugal is because the government subsidizes it. 
The official currency in Panama is the Balboa, but they all use the US dollar. The only Balboas you get here are in small change, which are coins. Otherwise, they use US dollars here all the time. The Greatest Lessons Learned By Living Abroad
My family and I moved to Central American in 2000 with the idea of blue skies and sunshine. Never heard of culture shock, never imagined or dreamed there would be a problem adjusting to our surroundings because everything we had read said that we would LOVE it!!! Much to our dismay, all that we had read was not exactly accurate. While my husband was in an office that had to speak English and my boys were immersed in football where they didn't care what language was spoken, my...
BANKING-- despite all their assurances that you have set up all the correct procedures and accounts, there WILL be problems. Not in your host country, but 'back home'. These will take the form of excessive fees, limitations on the maximum allowed currency, changes in their regulations, both Governmental and internal bank rules, staff changes, lock-outs for internet transactions and many, many others.