Yammer is not going away. Engage is just enhancing the experience, and the Communities app for Teams is being rebranded to Viva Engage.
See this article: Introducing Viva Engage - Microsoft Tech Community
Yammer is a key part of Microsoft 365 and Microsoft Viva and this change only impacts the Communities app for Teams & Outlook. The Yammer web experience and the native Yammer mobile apps will continue to be a part of Microsoft 365 SKUs and the same communities, storylines, and stories are made available through both Yammer and the new Viva Engage app. We are continuing to invest in Yammer and bring the powers of Yammer to Microsoft 365 and Viva.
For nearly ten years, Yammer has been a leader in employee engagement, and now we are delivering these superpowers into the Microsoft Viva platform to empower people and teams to be their best, have a voice, and feel included in the workplace. We know communities, conversations, cross-company relationships, and personal expression are critical to any thriving culture and organization – and essential pieces of employee experience.
Viva Engage will continue to show the same network, home feed, and communities that you see today in Yammer. Any content created in Yammer.com or mobile – including community conversations, storyline posts, and stories – will be viewable in Viva Engage. Likewise, content created in Engage will show up in Yammer native experiences. Viva Engage will also continue respecting any custom branding done for the Communities app. To use Viva Engage an organization must be licensed for Yammer.