If we update your configuration will Lambda function remains - Yes
Advantage and Disadvantages of AWS Lambda
List objects in S3 bucket - To get a list of objects within a bucket, use the Amazon S3 client's ListObjects method, supplying the name of a bucket. The ListObjects method returns an ObjectListing object that provides information about the objects in the bucket. Returns some or all (up to 1000) of the objects in a bucket with each request