@Nigel *********************
I think the legal implications would still be the same, whether or not the last day of stay is a Sunday. OP is permitted (I believe) to cancel work permit in advance (not sure how many days). Even if they go in ahead of time, the date of cancellation will be marked as the last day of extension of stay, not the day OP goes in. Best to cancel everything legally if there is a chance of returning at some point in the future.