Beginning September 30, 2018, Visio Web Access (Visio Service) and its Web Part for SharePoint Online will no longer be available. Instead of Visio Web Access you will be able to use Visio Online and to migrate your organization’s web parts to a newer experience with the new Javascript (JS) APIs for Visio Online. Visio Online enables high fidelity viewing, sharing, and collaboration in your favorite browser, without installing the client for all Office 365 licenses. It supports embedding Visio diagrams in SharePoint Online using a modern file viewer web part and with IFrame along with JS API programmability.
How does this affect me?
Beginning September 30, 2018, users in your organization will only be able to view Visio diagrams in their browser, but not create or edit. Visio Online viewing is available to most Office 365 subscriptions.
What do I need to do to prepare for this change?
iFrame with Visio Online APIs instead of Visio Web Part with Visio Services JS APIs
I will be preparing a part 2 of this blog post on how to implement the above stay tuned.