There is no automated migration from SharePoint possible, but having the existing application makes it easy to migrate the logic and data.
If you need to refactor multiple Sharepoint applications, it will make sense to analyze them to see if you can reuse components from one another. Suppose Mendix refactored applications and Sharepoint applications will co-exist. In that case, you can look at Java libraries allowing you to create Java Actions. Integrations using REST API calls are possible too. One of many examples you can find here: https://gitlab.com/quantr/sharepoint/Sharepoint-Java-API
Go make it