index.max_result_window is set on the Elasticsearch server side, Hibernate Search has no idea how large it is. So no, you can’t retrieve its value from Hibernate Search.
You might be able to retrieve it from Elasticsearch by querying the settings using the unsupported direct access client provided by Hibernate Search, but I would recommend just setting consistent values in your application and your Elasticsearch cluster.
Just in case, here is the section about this exact topic in the documentation: paging and scrolling. Just a word of advice: if the default value of 10000 is too low for you, you’re very likely to experience performance issues at some point. You should probably change your application to never, ever load that many elements: use scrolling for batch processes, and paging with a reasonably low value, e.g. less than 1000, for displaying results to users.