No.

It’s fine.

Just don’t post things you don’t want saved forever.

Its the same as when you say something in meatspace that you cannot undo either

you can delete notes on Satellite web client, but you might find your deleted notes saved by other relays when you use other clients. It's on their disclaimer when your purchase their relay service: note deletion requests are not guaranteed

so, you can delete, but the task to have it deleted everywhere 100% may be humongous

Not entirely true, when u delete an post ( with an client which supportedthids like amethyst) , an query will be send to the relays that the post should be deleted but its not mandatory the relay has the possibility to ignore this.