I think that rule would work, one option would be to have maybe the next generations heir complete that job opportunity or a succession of the next few generations (ie....some city halls have 2 or 3 opportunities in them, so the next 2 or 3 heirs must cover each job).
We are anxiously awaiting the birth of our first child (Beau and Zoe)...
http://lvlt.thesims3.com/sims3_asset/sims3_asset/media/shard000//shard000/299/642/016/00/screenshot_original.jpg
Also notice we moved to Barnacle Bay after a T5 tornado went thru our town (also known as error 12 :) ).