It can. Every sentence of an answer is numbered to the card it came from, so you can check. If nothing matches, it is built to say “no answer”.

Yes. Once Apple Intelligence is set up, your cards, search, and Ask work without a connection, in aeroplane mode too. Saving a new link needs one, to load the page.

Saving still works. New things are kept and read once there is room, in the order you saved them. Until then you find them by their title, file name, or link.