(Just to clarify: Those Discussions are for advices. If you want to reach the official Fandom Staff, use https://fandom.zendesk.com/hc/en-us/requests/new )
Preventing some code from saving is very unnatural for the MediaWiki software. There are filters to prevent vandalism and spam but not for content mistakes.
There is a tool named TemplateData that can tell the user which parameters are required, but it's just giving information, not enforcing it.
You can also put an error message as the default value of that field, so if no value is given, the error message will be displayed on the page, reminding users to complete the information.
Technically, it's possible to make the template not showing up at all if a given parameter is missing (it will be saved but has empty output). However, this too is not recommended, as users will be confused and won't know why it didn't work.