Here's an article about the last episode of St. Elsewhere that I remember seeing on Channel 7 (I think):
I don't know if this is the same as the "Last One" episode with the unusual plot twist because the last scene I remember watching on TV was the hospital being torn down.
You missed one entire season. The second to the last season ended with the hospital apparently being demolished while Dr. Auschlander was trapped inside. The last season opened with the hospital saved from the rest of the demolition by a buy out from a company that I think it was called "Ecumena."
And it makes me sad that I actually know this information without having to consult Wikipedia or IMDb.