It is unlikely they will preserve that long. The plants are usually sold bare root and dry to induce them into a sort of dormancy.

I never tried it so can't say for certain, but the instructions I always got with the onions I ordered was they didn't have to be planted immediately, but nothing suggested the would last several months in that condition.

I think that username missunderstood your question. If you can keep your sets dry,cool and in the dark, well ventelated, give it a try. All you have to lose is a few sets. I kept some all summer and most did not dry out too much to sprout in the fall.

I buy enough sets in the spring so I can plant a couple dozen about every 1 1/2-2 weeks for a continuous supply throughout the season. I store the sets in my spare frig in the basement and lose very few. I buy in bulk so I only get the sets with no green sprouts. Seems they keep better.