And how and when would the Assembly chose which legislator does so? Who will determine any election related disputes or otherwise make sure processes are correctly followed?
The simple reality is that someone actually has to administer an election. The idea that the region should have a designated official to administer all elections except one which instead will have a different process where someone else will be “chosen” in some undefined, unexplained manner is not only ridiculous but a court case waiting to happen.
What happens if the successor flakes? Perhaps a line of succession would be better fitting? Otherwise, I’d be more in favor of the resignation causing a collapse of government and triggering snap elections.