I sent an email to riot support to ask them when the Halloween skins would leave the shop, since the date was very uncertain and no one really knew.
Their response back was as following :
Thank you for reaching out to us!
The specific set of skins will be available in the shop until the 21st of November!
If you have any other questions, feel free to ask away!
"You merely adopted the dark, I was born in it. Molded by it."
Player Support Specialist
Basically the skins are not available to purchase in the store anymore, and a rioter gave me the wrong information is there anything I can do about it?
Second response https://imgur.com/BpkeWaD
Last response they gave me https://imgur.com/KaPhGNP