I believe it is pretty stable shape-wise as it warms up. I've seen plenty of marzipan that isn't refrigerated; I think it will be fine. Even the online recipes for homemade marzipan say that it does not need to be kept cold. The marzipan animals that ship from Germany survive that ordeal without problems, so I wouldn't worry about a bake sale.
“Assuredly it is a great accomplishment to be a novelist, but it is no mediocre glory to be a cook.” -- Alexandre Dumas
"I give you Chicago. It is no London and Harvard. It is not Paris and buttermilk. It is American in every chitling and sparerib. It is alive from tail to snout." -- H.L. Mencken