for my personal experience, you need 2 licenses (split your current license or purchase a new one for AWS).
Duplicating the environment is not a good solution because you will have 2 qmc, 2 systems to maintain and if you split the license you can lose some efficiency in the Access Logins Tokens.
I believe also there is a hybrid solution base on a Qlik Sense cluster partially on Premises and partially on AWS, but it sound to me as a complicated solution, and I never had the courage to try.
I finally chose to move everything on AWS (Redshift, S3, EC2). I cut my cost of 60% and got more speed and reliability. My AWS big data specialist show me also the new generation services that will improve drastically the performance and reduce the cost: Athena (Serverless queries on S3 to load the data without using Redshift) and Glue (new AWS integrated ETL tool).