But Christian said everything happened. So was that supposed to be Oceanic 815 or the plane Lapidus was flying?
The entire flash “sideways” in the show occurs after they are all dead. Some soon; i.e. Boone. Some later -> Jack. Some waayy later -> Hurley (how many hundreds of years later), the new “Jacob” was semi-eternal.
The reference to everything that happened, happened was the dialog between Hurley and Ben “You were a great #1. You were a great #2” means that Hurley and Ben were the replacements for Jacob and Alpert. Even the semi-eternal die eventually.
They all eventually died and that trigger brought them all together in the afterlife. Why? Because of the shared experience on the island and the love that they had for each other. All of them, even Ben.
To answer your question: The plane at the end was Lapidus’ plane carrying Miles, Alpert, Kate, Sawyer, and Claire off the island and to points unknown. Jack dies at that point when the plane flies over.