Not sure if they will survive whole, but we chop our excess onions raw, unblanched (and peppers, mushrooms, carrots, etc) and have no trouble using them . Best used fried from frozen on a fairly high heat - but for stews etc can just be thrown in at the start of cooking.
Freezing is all about water content, and the destructive effect on the cell walls that the water has as it freezes - the faster the initial temperature reduction the better, slower chilling results in slow, steady expansion of the water molecules, thus rupturing the cells of the item being frozen, leading to a mushy end result - tomatoes, having such a high water content are a bit of a no-no, although if de-seeded and diced can work quite well, but again only suitable for cooking with once thawed. - I would certainly not defrost them - they will go mouldy and rotten, put them in the freezer and after 48 hours or so get one out and try using it - that way you'll know sooner rather than later whether you can salvage them or not.
Bon chance !