for Skype for Business
The official word is that Teams is a single client experience to handle many functions within Office 365, one of which is Skype for Business (SfB). Much like how you can access Word and Excel via Teams, SfB is still a stand-alone product, but the features of which are available in Teams.
“There is no end of support date at this time” for Skype for Business
Having Said That...
As the functionality transfers into Teams, along with user adoption, then logic would show that Skype for Business (online) certainly seems to have its days numbered.
Microsoft has outlined its roadmap for transitioning Skype for Business (SfB) to Teams, suggesting you:
