I hate the damn things and rarely use them, but what are the practicals
of using them please?...

I used to have a phone, which I could set to require a delivery
receipt, or maybe confirmation of delivery. Not seen a phone with the
feature since.

Out in the sticks at the moment, with a poor to none mobile signal, she
is sending questions by text and text answers which don't match the
questions.

If the phone gets 'text sent' rather than 'unable to send' - does that
mean the text is on the network and will remain on the network until
delivered? Getting delivered the next time the target phone appears on
the network?

Do text messages time out if undelivered for a period of time?