Keep in mind that we are talking about one of the banks that were at the forefont of the 2008 financial crisis. They would have gone bust if the US wouldn't have injected billions of dollars into them. They are one of the reasons why Bitcoin entered the stage to begin with. They are not to be trusted.
As far as custodial obligations go, Goldman has nothing to do with it. It's not like they can freely dip into Circle's trust accounts and siphon customer deposits into investments. Goldman has plenty of other assets they can legally gamble with. If Goldman goes bankrupt, Circle's custodial liabilities can't legally be used to pay other creditors. This is a non-issue.
No thank you.
From where I stand, insolvency as a matter of business operation is not a concern whatsoever. Insolvency because bank accounts were seized by the U.S. government is the issue. Tether is much more likely than Circle to have funds frozen or seized.