- I had a hairy egg and now it's gone?
- This egg drops a mount and I've had it for days but now I don't have it and I don't have my mount
Eggs that hatch after a certain amount of time will age in real time, rather than when your character is logged in.
This means they can hatch while your character is offline. If this happens, the loot that is inside the egg will be pushed directly to your bags. You'll see the item icon pop up over your bags like normal, and you'll see a line in your Chat Log showing what your character received.
However, these can be easy to miss in the rush of information and chat your character might receive while logging in.
Eggs can drop a variety of items, and while some are Rare or Epic quality, some drops will simply be gray or white quality, and hard to pick out in your bags. If you can't pick out what your Egg dropped, you can use WoWhead to see what other players have reported as drops from their Eggs, and then use the Search feature in the backpack window to see if you recognize anything that dropped. Keep in mind that WoWhead may not always have accurate information, and you could always find something new from your Egg that hasn't been found yet.
Another thing to consider is that if you had received a gray vendor item, you might have already sold it without realizing it.
Note: If your bags are full when you log in, the Egg's contents will either be mailed by the Postmaster, or will pop into the next empty bag slot the next time your character logs in.