Again I ask, how many (if any) people have withdrawn 1 million in Bitcoin and actually got cash? Bitcoin has no worth until you either use it to buy goods and services OR you get cash for selling it.
I'll try to answer this one more time. Billions of dollars of BTC sells every day. Every seller (obviously) receives cash in return for the BTC they sell. Every person who buys the BTC of course needs to pay in cash.
Coinbase, which is about do to an IPO, will provide exact details of how much money they take in and pay out each day (along with their margins). You will see in their offer prospectus that the amount of money they are making on commission on a daily basis is staggering. You can take a read of that yourself.
I only know one retail investor who sold all BTC at once. He received USD 2m, in cash, in a single transaction. But I know many who have sold (and received in cash the USD 50-100K range). Remember, most retail investors who hold larger amounts won't typically sell all in a single transaction.
I know one OTC operator who sell around USD 100m per day (meaning they both take in, and give out 100m in cash on average, on a daily basis).
You can buy whatever good or service you like by paying in BTC provided the seller is willing to accept BTC. Or you can simply use the cash you get, and then buy whatever good or service you like by paying in cash provided the seller is willing to accept the cash.
More sellers than ever are eager to get their hands on BTC and so are willing to accept it, but either way, later this year we will see both PayPal and Square, among many others, allowing you to have an underlying storage of global in BTC in your account, but from a "user-experience" perspective, you will be able to pay for any transaction either in cash (which is then reconciled in your account in BTC), or in BTC directly. So, for a merchant it becomes seamless, as a BTC transaction to them appears as a fiat currency transaction, but it actually is being converted and deducted from a person's BTC balance in the backend. If the merchant wants BTC they can ask for that. If they want cash, Square and PayPal will convert BTC into the amount of cash as is needed.
Are there buyers of BTC who refuse to pay you cash? Yes of course that can happen if you get scammed or are an idiot (just like a buyer of any other item can refuse to pay you cash). Are there banks or exchanges that go bust or make errors or scam you? Yes, that can also happen (which is why its not advisable to keep BTC on an exchange, and, if you so want to sell via an exchange, make sure its a regulated exchange.
The last question, which is maybe what you are actually asking, is does a bank have to accept the cash you have received from the sale on an exchange. The answer to that is that it is up to the bank. I, and many of my friends in finance, have established relationships with banks, such that a transfer of a million dollars in would be accepted no problem. But if you had no track record, no prior establishment of wealth or legitimate source of income, no KYC compliance etc, than any bank's compliance department would raise an eyebrow at a sudden appearance of 1m incoming (regardless of what you supposedly sold to get that 1m, whether its a house, a lottery win, stocks, an inheritance, or BTC). They might well want an assurance as to the legitimacy of that income, depending on the bank and the applicable jurisdiction. So, for example Switzerland, HK, Singapore, Cayman Islands, Spain, Monaco, etc no problem at all. Whereas in the US likely you would be questioned.
Hope that helps. If you ask legitimate questions, with specific details, I will try to answer for you.
