I don't have much else to add, except that I was wrong; the Helicomatic is indeed technically a cassette rather than a freewheel, as the freewheeling mechanisms are housed in the weird splined/tornado-looking jawn. Sorry if this caused any confusion. Also, to reiterate what I said above: if you bring that thing into the typical bikeshop, they will sell you a new wheel.
Again, this is only true of the Helicomatic models. Maillard did, indeed, make traditional thread-on freewheel hubs, but a mid-80s technium would be a prime candidate for the Helicomatic hub...