Starting now for first release tenant and then mi July, Yammer is integrating with Skype for Business. Finally Microsoft is really integrating Yammer with his own product and start replacing duplicate features with the best.

So the Yammer IM chat is going to be removed and you will get the Skype icon in the navigation bar – the same way you have Skype for Business integrated with Outlook Web Access

Navigation bar in Office 365_C3_201753095040