I have got a 3 kg pack of raw wild unheated honey. Expiry date is 18 months from packaging.
What is expected to happen to it after the expiry date? Will it be edible?
It is probably a best-before date (possibly regarding crystallization of the honey or other cosmetic changes), and should still be edible afterwards.
Most honey has historically been stored raw, it is still sold in the comb in places, and has still been known for having a long shelf life if left in a closed container. Honey has mild antiseptic qualities, and too little water, for most anything nasty to grow in - usually the heating and other processing has more to do with appearance and texture (crystallization and cloudiness, and also batch consistency and efficiency), rather than specific safety concerns. And if it does go bad, from exceedingly poor storage, too much moisture, or something of the sort - it should be very apparent, and on the surface only.
That being said, if you have concerns about your honey specifically or believe that its raw nature poses more risk - you should act as it seems safe for you. Putting the honey in the fridge should double the shelf life, at least, though it will also encourage crystallization.
This is a little info which would go a long way to help you decide if you should use honey after expiry date.
How long can you keep honey?
Honey found in Egyptian tombs was still good after 2,000 years! Honey does not spoil unless it has too high of a water content. If you see signs of fermentation that honey could be spoiled. I keep honey for storage in glass canning jars because it is easier to warm the honey when it granulates.
Can honey go bad?
So, yes, honey mostly doesn't spoil. However, honey can contain spores of Clostridium botulinum. This isn't harmful to adults and children over one year old, whose gastrointestinal tract is developed enough to deal with the spores. But children under one are at risk for infant botulism, so honey is not for your infant.
Honey doesn't expire. It's the only food that doesn't. However, you should never feed it to children under the age of one regardless of its freshness.
If you find that it has crystallized, you can microwave it to re-liquefy it, but make sure you do it in very short intervals; as little as ten seconds at a time, and never in a plastic container. Sugar heats up quickly and much hotter than other liquids so it will melt through your honey bear before you can say just right. If you want to heat it in the plastic container, heat up a container of water big enough to hold the the honey bear with a little extra room. Then place the container in the hot water to liquefy the honey.
I've yet to figure out under which conditions it crystallizes and which it doesn't, but I'm sure there's some trick to it. I do think that temperature has something to do with it, but I've had honey crystallize in the summer and stay liquid in the winter, so who knows.