Update, finally got around to pulling the valve cover and turbo/exhaust manifold. Cams are clean, plugs still look good, so at this point I have no idea what actually failed. My theory of a busted oil line was incorrect, both lines were still on the turbo tight and are intact. It looks like the fuel line which runs from the firewall to the rail was where the initial failure happened. Turbo has practically no shaft play and fins spin fine, only very minor damage to them. Main problem is tons of corrosion from the layer of fire extinguisher dust, but a bath and a rebuild and I think it'll be good to go again! Probably need a new wastegate though, it's pretty f-ed up.