How do we do that correctly? OnDisappearing does NOT mean the page is being disposed, it just means it is no longer the top page. In other words if I have a mainpage on the screen and then I push a detail page on top, it will call the OnDisappearing for the mainPage and the OnAppearing for the detailpage. In this very common scenario, I would not want to dispose of anything on the mainpage because as soon as the user clicks Back, I will be seeing the mainpage again so I don't want to dispose of it.
Perhaps you are saying for the OnAppearing event to always create the SyncFusion datagrid and the OnDisappearing event to always dispose of the syncfusion data grid. I suppose that will work, but would be a lot of unnecessary destruction and creation of datagrid as pages are pushed and popped on the Navigation stack.