Changelog for update GOG-9 (Mac) (added 03 November 2015):

- We've updated the Wineskin wrapper for the Mac version of Evil Genius to be compatible with OS X El Capitan.
- The updated DMG file will not require disabling the System Interity Protection feature found in OS X El Capitan.

The day I bought it I had not trouble playing it. Then the Mac system was still Mavericks, since I updated to El Capitan the game launches onto a black screen and then closes immediately without any crash or anything else at all for that matter.
I really wish there was a way I could go on playing it I hope you can help

Sorry, I can't help you. I just copy the changelogs to the respective game forums to make them visible for everyone.

I would say you should contact support and tell them about your problem. They should be able to help you.

https://www.gog.com/support/contact/technical_issues_with_games/evil_genius