I have several marriage certificates where a father was not marked as "deceased" even though he died anything up to 20 years previously.
On the other hand, I have also been able to prove the non-decease of a father from a marriage record in a parish register, because he was one of the witnesses, and there was his signature bold as brass. It has long been customary for fathers - particularly the bride's father - to be witnesses to the marriage if they are still alive. So this can be a good way to prove a father is still alive. If he was not one of the witnesses then this does not disprove - but it raises a certain presumption that he may have been, and should perhaps act as a prompt to search for a death prior to the date of marriage.