I wrestled with 2012 for a couple years and then with Seirra v. 25 was finally released and I upgraded. Don't know the details, but it's essentially true that Finale dropped support for 2012.

You can try using it with Human Playback disabled. There are other issues, however, so that may or may not work for you. If you have older 32bit only music fonts installed, they can cause crashing, too,

Bottom line: 2012 does not work properly in Sierra and is no longer supported.

http://www.finalemusic.com/blog/compatibility-with-finale-notation-products-and-macos-sierra/ 

I work 2012 on Sierra. What issues are you having? If it's playback related be sure you switch to "Play through Midi" under "Midi/Audio" menu. If you really need playback with Audio Units then your only option is to upgrade. I only use Finale for engraving work and 2012 has been working well.