As I know The sheetid shouldn't change when you move the app to another server or publish to a stream or even duplicate the app. Every time you create a sheet, a new unique id is generated and cannot be changed.
hi Meghan, to my knowledge a function returning the sheet id has not been delivered or documented on Qlik Sense Saas...
Just a practical limitation example: To ease navigation on a Saas solution and configure a "go to last visited sheet" (the client want his filter on another page),i had to set up a set variable button and store the id of each page manually.... Problem is: the app keep getting new pages and the only solution we got is not viable on the long run.