Even at his level retirement is a process that would take several months at a minimum and could be a year or more, depending on exactly why he's retiring. Planned retirements tend to be planned well in advance and worked around various service calendars regarding when promotions are done, time in grade, and a slew of other thing; if there's medical reasons it can be done quicker but overall it's not something that can be done on the spur of the moment. Just setting up the transition for his replacement will take time unless its being done for emergency reasons (and given his importance, even 'heart attack' might not be enough reason to skip everything).
His active duty ID would be exchanged for a veteran's ID. Dog tags are his property to keep, plenty of people keep wearing them as they're not official identification or anything like that.
Retirement in the US Air Force