A lot of times I write a response without much thought to it and then I look back and realize I could have made a lot more sense. Looking back on my last response, As Time Goes By and Keeping Up Appearances are the most realistic shows to possibly make a comeback.
Allow me to do some math and please excuse me if I am off a bit. Both of these shows were in the 90's. During the time of filming, the main characters of KUA were roughly the age of Summer Wine's trio during the Blamire years, so perhaps today they would be around the ages of the guys in the early Truly years. As I previously mentioned, over the years I have developed a love for the character, Richard, and Clive Swift in general. However, I read the Patricia Routledge resents the role of Hyacinth because she doesn't want to be remembered for a slapstick role and wants to be known for more serious roles.
OK, Lionel and Jean of As Time Goes By appear to be roughly the age of the trio during the Seymour years. So now that might make them around the age of the guys during the Hobbo years. Now that is pretty old, however, i could imagine rather elderly couples being quite funny. Lionel is a bit of a socially aloof, grumpy at times, character. I could see those traits develop further over the years. Lionel and Jean would be great with grandkids and Allister could still get on Lionel's nerves. Add an elderly Penny and Steve to the mix and that is definitely a great combination. Although I imagine Judith Dench is occupied with biggerr things.
Anyway, after further reflection, these are my favorite shows in which a comeback is most realistic!