Vignette about to expire but the passports are still with UKVI

Guys,
I applied for tier 2 visa with my wife and daughter on 27th July. The decision on all 3 applications were made on 14th August and I got my passport back on 16th of August. The vignette sticker had date of 18th august to 17th September. However, my wife and daughter are still waiting for their passports till today 11 September.

I travelled to UK and collected my BRP. I asked the post office to check if the BRP of my wife and daughter are there and they confirmed that they are there which means the visa has been granted. Since the date of decision is the same as mine so I presume that the date on vignette will be the same as mine.

Now since they have not got the passports. What will happen if they get the passports after their 30 day vignette expires. It's not our fault, UKVI did not return the passports to them to travel.

Thank you!

Anyone?