Awaiting mortgage decision at bottom of our chain

Hi all I wonder if someone could put my mind at ease...

Within the space of a few days, we found the house of our dreams, and we accepted a private offer on our house from good friends. They had a FTB waiting to buy their house so we had a complete chain! On that basis, our offer on our dream house was accepted. Happy days!

Then our friend's FTBs submitted their full mortgage application and the credit check flagged something from the past regarding a phone bill (which the FTBs said was the phone company's error). Halifax requested a letter of explanation from the company. Apparently, the phone company sent a letter saying their records didn't go back far enough, so Halifax requested some other documents. These could not be produced, so Halifax have said they'll come back with a decision.

This was a week ago, and still no word. I'm tearing my hair out, because I've already forked out for a survey and mortgage application for a house that we may now lose.

So I'm wondering...
Do they stand little hope of being offered the mortgage given they couldn't produce requested documents?

Is a delay a good thing? Surely a decline could have been given straight away.

Does anyone know how long halifax are taking to get back with mortgage decisions?

Thanks for anything!