Is AFP slated to be removed from future versions of macOS?
Apple Filing Protocol is deprecated1, not "dead".  There's a big distinction and that is being deprecated, it's still included and still works at the time of last development but it has been superseded by something else - in this case SMB2.  It also means there will be no further development. 


  Will it stop working in future versions of macOS?


There will come a point in which Apple no longer includes support for a particular protocol or service.  Only Apple will know this for certain.


  Can I safely use AFP without worrying about it "dying" on me?


AFP is not going to die the same way cron didn't die when Apple went to launchd.  If you are running AFP today, you will have AFP tomorrow.  It won't be "upgraded out".  That said, Apple can decide tomorrow that future versions of macOS will no longer come with AFP; that won't break your existing macOS installation.

What all this means is that as a deprecated protocol, manufacturers are going to stop including support for AFP in new products (like NAS devices) and systems admins should begin making plans to switch over to newer technologies.  Also, being deprecated, it's no longer the default file sharing protocol meaning you will (eventually) have to take explicit steps to enable/connect to AFP shares.

It's important to note that AFP does not support the new APFS (Apple File System) so newer versions of macOS (Sierra going forward) will not have the ability to serve AFP shares.2  


  You can share APFS formatted volumes using the SMB network file sharing protocol. The AFP protocol is deprecated and cannot be used to share APFS formatted volumes.


Though, they will probably include the AFP client so it can continue to connect to legacy devices/systems.



1 Deprecated refers to a software or programming language feature that is tolerated or supported but not recommended. A deprecated attribute or feature is one that may eventually be phased out, but continues to be used in the meantime. Deprecation also helps to ward off backward compatibility issues, giving users time to migrate and begin using the newer recommended feature. The deprecated feature will continue to work in the current environment, but will show a warning message that the feature being used may be removed in future releases.  Source:
  Techopedia.

2 Source:  9to5mac.com - Apple File System (APFS) announced for 2017, scales ‘from Apple Watch to Mac Pro’ and focuses on encryption