the new style racing
sails i have seen are kevlar and mylar. i have had bags made of this so i can see how it would hold up--it doesnt. after the teams have used them up,mebbe 2 more or 3 more years, and pricing isn't low enough to make that work.
bedsheets--a good idea--but they may not be worthy of 50+ kts for long...could blow out fast, like a blue tarp.....
when new boats come with north triple stitched sails and the new owner wishes to get new--hell i will gladly spend my hard gained dough on the old ones.
if a sail blows out at sea--there is something on board that is usable to make a jury rigged one--plastic tarp, bedsheets, anything to get you to a place where there is a loft or a sewing machine
even your boat cover is usable.