It may be possible to get it un-seized, but I would bet that it is smoked from the overheat.
What was your coolant level before the incident on the Highway? Do you know? You may not know, however, the pressures can get extremely high in a coolant system, in an overheat. If it was low, the pressure may have gone sky-high. This may be why the freeze plug blew.
Recently, there has been an increased demand for these engines (imagine that!) I believe it will be difficult to procure a replacement, and of course this will drive the price up as well. I think these DII engines are a big problem for the Land Rover name.
oneohsix, Where are you located in the US?
"I can't believe I'm sitting here, completely surrounded by no beer!" -Onslow