Blogger has disclosed What will Happen To Blogger's Google+ Integration When Google Shutdown Google+ In March 2019. According to the notice shared on the blogger dashboard, all google+ share functionalities will stop working with effect from 4 February 2019. Checkout the notice below:
Following the announcement of Google+ API deprecation scheduled for March 2019, a number of changes will be made to Blogger’s Google+ integration on 4 February 2019.
Google+ widgets: Support for the “+1 Button“, "Google+ Followers" and "Google+ Badge” widgets in Layout will no longer be available. All instances of these widgets will be removed from your blog.
+1 buttons: The +1/G+ buttons and Google+ share links below blog posts and in the navigation bar will be removed.
Please note that if you have a custom template that includes Google+ features, you may need to update your template. Please contact your template supplier for advice.
Google+ Comments: Support for Google+ comments will be turned down, and all blogs using Google+ comments will be reverted back to using Blogger comments. Unfortunately, comments posted as Google+ comments cannot be migrated to Blogger and will no longer appear on your blog.
According to google if you have used your google plus account to register for other google products, once google plus is shutdown you will be directed to use google account login to access other google products.