There is a function in Episerver that informs an editor that he's about to delete a page that other pages link to. Is there also a function that informs the editor if he's about to delete a page whose body text etc some other page gets/uses (dynamic function)?
If there is no such function, how can I create one?
You can add custom logic to override the content events in Episerver, please see: https://world.episerver.com/forum/developer-forum/-Episerver-75-CMS/Thread-Container/2016/6/in-episerver-8-how-can-i-override-the-publishsave-event/
How you would fetch and check the usages of the text however, I am unsure. If you had the re-used content in the form of blocks you could do like Ryan Vux explains here: https://world.episerver.com/Modules/Forum/Pages/Thread.aspx?id=188500#188563 and warn the user if the timesUsed > 1.
This function is postponed by the customer. I'll take a closer look then and let you know how it goes. Thank you very much for your reply!