Normally I wouldn't do this, but if onions were not infested and crop of leeks is not super-important for you - why not to try? Next year you will plant something else there...

Thanks!

I'll probably try it just because I'm too tired/lazy to get a whole other bed set up.

Robinsons, in England, who grow award winning onions as well as producing seeds for exhibition, heritage and general edible use, have been maintaining a 200 year old onion bed. I, myself, because of endemic white rot on my plot, have a raised bed area where I grow garlic, every year. While crop rotation is a precursor to plant health, it is only one strategy out of many and for some crops (most notably beans) a permanent trench system has been in use for centuries.

I also committed the cardinal sin of growing potatoes in the same place for 2 successive seasons (and am still waiting to be cast down into purgatory by the god of gardening). Go ahead, Bart - life is too short to get hung up on everything....if it works, great and if not, well then, a lesson learned....but who is harmed by your little experiment?