Your personal account will become your joint account and his old account will simply go dormant. Before he forgets how to access it he should log in and download all the PDF & .taxfiles to save for the future. You should do the same ... save them all to a removable storage unit like a thumb drive to keep them safe and have them available anytime you need them.
Also ... once you file a joint return keep the positions the same going forward ... switching positions on a tax return confuses the IRS so don't do it.
