I hope that is right, but i have also seen articles that they are removing the Passive Voice checking, and maybe already have from the Mac version. The thread linked below was originally a Mac Word thread, but I think some of the posters were commentiong about Word 2016 in general. So I hope it does come back, but I am a little skeptical that your post is not specifically talking about the passive voice checking. PS - i marked your solution 'Accept as Solution' and it put a big box saying it was a Microsoft Verified Answer, although neither of us work for Microsoft I don't think!
How to Add Microsoft Word’s Passive Voice Tool. Before you can use the passive voice tool in Word 2016’s Spelling & Grammar check and the readability statistics, you have to add it to your proofing options. Select the File tab. Select Options in the Backstage view. Select Proofing in the Word Options dialog box.