The counterparty risk is not so much that your ETF provider could go bankrupt. Since the stocks in the ETFs belong to the investor (you), they would not be lost in that case, provided that your ETF provider actually upheld the law. The ETF's counterparty risks are mainly fraud, securities lending and derivatives contracts.
Fraud:
There have been cases in the past where investment firms or their employees secretly and illegally sold their customers' assets to pay their bills, e.g. to avoid bankruptcy. In that case, your stocks might be gone and you would have to sue the investment firm, hoping that there is enough money left to pay for the money value of your lost stocks. In some countries, there are (limited) government insurance schemes against this risk.
Securities lending:
Most ETFs lend their securities to hedge funds for short-selling. The hedge fund pays a small lending fee to lend your stocks e.g. for a week. It sells the stock immediately, and hopes to buy it back after a week at a lower price to return it to your ETF. However, if the hedge fund goes bankrupt in between, your stock will not be returned. For this reason, the hedge fund has to leave some collateral at your ETF. Losses occur only if the hedge fund goes bankrupt *and* the collateral loses value at the same time, which might happen during times of great market turmoil.
Derivatives:
Sometimes, ETFs invest part of their money in derivatives instead of buying stocks. These derivatives are issued by some bank; if the bank goes bankrupt, the invested money in the derivatives can be lost. As for securities lending, there might be some collateral, but it is not guaranteed that this collateral will keep its value.