re: Are there more option or customization available for the premium templates?
How do you mean???
re: By the way The search functionality was on the site for the past several months then vanished.
Then it must have been added by another means … perhaps custom coded or something or maybe you do own a premium template???
re: The admin still shows it.
Correct, it always has been.
re: Was there a change in the plug-in? to force buying a template?
No, free features have ever been removed, making them pay only. Search in the frontend has been a feature of the premium templates.