I'd guess that the cloth will fall off, although I've never had to epoxy upside down while building a kayak. Does Wooden Boat magazine have a BBS that caters to builders of larger boats? If so I'm sure that they have encountered this problem before as it's much tougher to flip over a 30ft. sailboat than a 17ft kayak.

I also suspect that the weight of the cloth might play a role. A very light cloth that didn't require a lot of epoxy to wet-out might stick, whereas a heavy cloth might not. The saturated cloth is the weight that is pulling off the surface. The tensile strength of the uncured epoxy is what is holding it on.