I am not sure what do you mean by dead.
As long as you know Sync Framework Toolkit is not supported and you know the consequences of using it.
As to Sync Framework SDK
Some Federal agencies did approve the usage of that SDK.
This link might be the answer to your question.
According to the US department of Veteran Affairs
https://www.oit.va.gov/Services/TRM/ToolPage.aspx?tid=11403
Microsoft Sync Framework Software Development Kit (SDK) Technology is approved with constraints in 2019, 2020, 2021
Approved w/Constraints: The technology/standard can be used within the
specified constraints located below the decision matrix in the
footnote1 and on the General tab.
However, these constraints are not met.
Technology must remain patched and operated in accordance with Federal
and Department security policies and guidelines in order to mitigate
known and future security vulnerabilities.
You might notice this announcement which does not seem to still be valid,
Microsoft Sync Framework 2.1 is now in extended support!
Starting from January 12, 2016, Microsoft Sync Framework 2.1 (including SDK and redistributables) has entered extended support. This change has an impact on how you receive software updates and support for Microsoft Sync Framework. For more detailed information, refer to the Microsoft Support Lifecycle.
I hope that can be an acceptable answer to your query.