I gather that what you mean is that the property has been redeemed and the vendor's existing financier has released the original document of title to the vendor's solicitors, who have yet to pass it to the purchaser's solicitors or the purchaser's financier's solicitors.

There would normally be a time period for them to hand over the said documents failing which the completion date would be automatically extended vis-a-vis the delay. Am sure your solicitor can do the math and calculate the delay. If the delay is from the vendor's side there's nothing to worry. 

Barca made my day