We would recommend to use a child theme when what you are trying to accomplish requires a template customization. This allows you to make code changes that won’t be overwritten when an X update is released. If you are already using a child theme, you still need to update the parent theme. WordPress itself releases updates which would include bug fixes, patches, resolved vulnerability issues and may introduce new features and functions. It goes the same with the X theme. You can check out the changelog of what is included in the latest release from this link: https://theme.co/changelog/
Now, if you are wondering if your site would work or not with this new update, I would recommend that you create a staging site. This is very useful because you can test drive any X updates in the staging area, do the customizations and troubleshooting without disrupting your live site. Once everything is perfect, you can easily and flawlessly proceed the update in the live site. To know how to create a staging area, please check out these articles:
Hope this helps.