There is already a contractual agreement to wear the signature and avatar for the duration of a week inorder to get the payment, so leaving in the middle of the week already breaks that agreement and means you will likely not be getting any payment for that campaign.

If you do stay till the end of the week and have already gotten another campaign which you need to wear their signature, you should notify the manageryo know if he can check your post history first and clear you for the week's payment so you can change your signature, this should not be an issue for most managers.

In the end it's all about communication between all parties to ensure everyone is on the same page