Final answer:
The Liquid code will result in a blank output if settings.main_heading is an empty string, due to empty strings being treated as false in Liquid conditionals.
Step-by-step explanation:
The output of the provided Liquid code would be a blank screen if settings.main_heading is an empty string. In Liquid, which is a templating language used by platforms like Shopify, an empty string is considered false in a conditional statement. Therefore, the content inside the {% if %} block will not be executed, and nothing will be displayed on the page.