I seriously question this. I can imagine a situation in which a person could be deemed (temporarily) "incompetent" at law, and that would be grounds to deem the contract (and this is a contract) to be unenforceable. I suspect, though, that it would be a very high standard to show that, especially in a situation wherein the couple had been engaged for some time and always intended to seal the deal on the wedding day, even while sober. That being said, I'll certainly bear that theoretical loop-hole in mind...