I'll just be direct. It depends on what kind of mythology you follow.
1. Greek mythology -> real (One who have worked with them have explained their experience around)
2. Norse mythology -> real (Same as 1)
3. Celtic mythology -> real (though it depends on how many people still worship them, overtime they may be forgotten, etc)
Dunno, about other mythologies but as far as I know as long as Deities exist, their mythology will keep on living.
Forgotten means for people to not remember the mythology and the deities. Yes, there is much mythology in many cultures one can read. However, how much of what is around today is what was once known of them?
In Norse mythology the Goddesses are seldom mentioned, rarely are they main characters. Most of the myths and stories that survive are about the male gods, about battle and struggle. Many believe that this is because the Norse were a culture of Warriors. So there was no need for stories of any other kind. However, if you look at any culture, you will not find that ever member is of one particular persuasion or belief. I believe that over the years many myths have been forgotten. Some were purposefully thrown away others just fell away as they became of less use to society as it evolved.
Think of your life and the stories that are told by your family members, do you all remember the same events the same? do you remember events that others do not even remember even though they were a part of the event? This is the way that things work, over time things get lost. The more of the myths we lose, the less we know we are missing.
Most myths are allegorical stories, some myths are a mixture of fact and fiction, and others are closer to the truth. It all depends on who wrote them down- it wasn't the gods, but men and women- mostly men. They serve to teach lessons, hide hidden truths, and preserve the teachings of inner schools of thought. What is interesting to compare is the similarity between different cultures myths- through the similarities we may find some thread of truth.
Myths also conflict each other from area to area, for example there are many contradictions in Egyptian mythology, that doesn't mean that the Gods or the cosmology is wrong, it just means people either made mistakes or added their own personal flair to an already existing story.
The Gods are certainly real, the stories aren't always factual.
