You can cancel it at any time.
So, if the replacement part arrives and you are happy with it, close the case.
However, it does say the seller has sent you a label and you have to return it by 27th April.
So, if you have no part and no label by 26th you will have to decide whether to wait for the part or to ask Ebay to step in and push the seller to provide a label.
Otherwise, the case will close in favour of the seller and you will have an item which doesn't work, no replacement part and you won't be able to open another case or reopen this one.
"There are two ways to be fooled. One is to believe what isn't true; the other is to refuse to believe what is true.”
Søren Kierkegaard, Danish philosopher (1813 - 1855)
