And finally, is it unheard of for a big company to be interested in your product, look at your code, then laugh you off?
Part of the due diligence that larger companies will undertake before acquiring any software IP is to determine the provenance and licensing of the software. So watch out for any bits of code copy/pasted from open source libraries and check that any third party libraries you use are correctly licensed.
A big company may pull out of an acquisition at any time, even after performing due diligence. They will never say "Ha ha! It's because your code is rubbish" because an acquisition is a business decision not a technical one.
If they're acquiring you because you built a product that has great adoption in the marketplace (YouTube), but your code is spaghetti they won't care very much.
If it's based on revenue they really won't care.
In most cases your core team will be required to stay on at the new company long enough that any missing documentation will have had time to get written.