“Any information in your research on the transmission of such an event through the DC ties?”
Explain to me what you mean by that.
Ercot is not electrically isolated from the other grids. The ties are AC-DC-AC so that the systems are not synchronized and stability of one system doesn’t affect the other.
But the electrical connections are constant through the DC ties. The switches are not left open, they are kept closed to help stabilize power flow through an asynchronous connection. At different times of the day, power may flow one way or another, but the legal requirements require a balance of flow to/from, I think averaged over 24 hours.