It shouldn't be removed from the collection, for the simple reason of the collection bonus that will be removed clearly says on the bones on the collection, no ton the items, the item you are clicking on it is just a "link" of the real item that you cna keep in your inventory.
Up here, we can see the collection bonus itself says until the day it will last active, then will me removed from there.
Now in this second picture, we can see the collection bonus itself doens't say anything about a deletion or expiration like the other one, but the ITEM it does says, wich means the item the one you cna keep on your inventory will be deleted, not the bonus on the collection. Just like says on the next picture, that is the link to the item, just like when you link an item on the chat, the item will be deleted, but collection bonus shouldn't be.
Is the same case for buff scrolls, they are deleted on the maintance they have on the description, but if you use the buff, logg off before the maintance, and log bakc after the maintance is done, you will still have the buff on your character, but not the scrolls on your inventory, because that's what they are deleting.
That is what common logic says to me.