Don't think bands easily retire these days. Making music can be done from home and touring can be less extensive, but there's so much money to be made and most artists are used to the lifestyle of traveling, meeting many people etc. Nowadays it's more likely that band members die or fall seriously ill while active, but bands may even continue in one form or another when key members (or even singers) have passed away. E.g. Eagles, ACDC, Queen, Pink Floyd, and recently Van Halen, Pulp, Depeche Mode, De La Soul etc.
Hard to think that PSB will continue after one of them stops for whatever reason, but 'the other one' and the heirs that will then be the new copyright owners will want to keep the legacy alive. Cf. Prince who was all about being very in control about his output, but after he passed a flood of stuff from his vaults came out officially and a lot of 'FM' bootleg CDs you can buy at amazon.
And in the end all of these bands will be forgotten if there are no fans left anymore. But that's life.
But on topic: I do not think they will retire soon. They are still one of the most active legacy acts (in terms of new releases, tours and side projects). The Kraftwerk comparison is a joke of course; their last album is 20 years old, and even that was a reworking of a song that was at the time also 20 years old! Electric Café is their last album of entirely new music, which was released almost 40 years ago. SInce, Pet Shop Boys had their whole career