`mHash` was deprecated several years ago when Hash came out. Does Magento 2.2.7 need `mhash` in order to run?
Also, how critical is `imagemagick` to running Magento 2?
There is no release version 2.2.7 as of now for Magento. The version latest version is 2.0.7.
As per documentation Magento 2.0.7 require mhash.
You can use any one or both from gd and ImageMagick 6.3.7, I am using Magento2 with out ImageMagick , we may miss some image optimization features in terms of quality if we do not use ImagMagick (Note: As of now I have not checked this in the code base , so I may be wrong also)