ETF : What's It Worth ?

My information about Exchange Traded Funds (ETF)is from Investopedia. It is the leading source of financial information on the web. My opinions on what ETF's represent in actual value to holders are my own. According to Investopedia ETF's track indices. That would include but not limited to Standard & Poors 500, NASDAQ Power Shares (QQQ), commodities such as gold, oil, materials etc.But because they only track the ETF's don't actually own. Conversely mutual funds own actual shares incorporated in their respective indices. Consequently mutual funds publish daily the net asset value (NAV) of the fund. Exchange traded funds do not publish NAV's. Because they don't own the shares.Every shareholder of ETF's effectively rely on arbitragers to keep the price of ETF's roughly in line with the theoretical underlying value of the stocks or commodities or bonds that make up the index.So the value of the ETF that trades from second to second is what the arbitragers say it is. Shareholders effectively take the word of some unknown person about the fair value of the ETF's at any given moment. Obviously what the price will be in the next moment is not guaranteed by the arbitrager. This reality leaves open the possibility of the tail wagging the dog. The arbitrager may engage in a bear or bull raid in the ETF which could impact actual prices of the real shares that are traded on the exchange.Let's fast forward to an unlikely but possible scenario. Suppose the market crashes. What does an ETF shareholder really own? Legally the shareholder owns a tracking index.Can one cash that in any where? If a mutual fund crashes the shareholders own the residual shares in the fund.Those are actual deeds to real companies.