You can merge your package default config with the one published by the user

https://laravel.com/docs/5.5/packages#configuration

In your package service provider:

/**
 * Register bindings in the container.
 *
 * @return void
 */
public function register()
{
    $this->mergeConfigFrom(
        __DIR__.'/config.php', 'awesome_package'
    );
}

/**
 * Perform post-registration booting of services.
 *
 * @return void
 */
public function boot()
{
    $this->publishes([
        __DIR__.'/config.php' => config_path('awesome_package.php'),
    ]);
}

Then in your package you can simply call config('awesome_package.my_option') and it will take the user's published value if present, otherwise it will take your package config default value.

This way you don't force any publishing but you provide a way to override values if needed