Same Rules Apply
Emeritus,
In my view, if you were in a largely service setting you would be introduced and first addressed by your civilian 'handle'; Doctor, Professor, Sir Fred Emeritus, Sir Fred and Lady Penelope Emeritus. How you decide to proceed is up to you: "Please call me Fred". I do know a lady, however, who signs herself 'Mrs >>>>> %%%%% OBE'.
In a civilian setting, it rather depends on the gathering, some are very formal, others less so. As with much else, I find the services approach is much more structured and I feel more comfortable following the basic tenet: 'start formal, relax later'. It saves on the odd gaff.
At the risk of appearing a pompous old (f&^t) duffer, if there is somebody I know might be ill at ease or is in strange company, I do try to see they are looked after and introduced around. It can backfire, however, when you find yourself saddled with the local bore and he won't go away and nobody is going to help you out!!
O-D