Please read this discussion:
The devs have not said much about this.
They are open to new maintainers opening pull requests to move the repo to a user that will maintain the plugin from that point onward.
Somebody needs to try to contact the original developer.
This has already happened with the Footnote Shortcut plugin, and will happen again soon with the Pandoc plugin(once a few issues have been fixed)
What makes you say that Templater is no longer maintained?
Looks quite active to me.