I will be dismantling a wonderful train display as part of an estate liquidation. The track and everything else is secured with screws/ glue as well as wired for lighting. Any advice or resources would be greatly appreciated so we do as little damage as possible.
First off, while there is plenty of value in a layout, the actual layout itself is usually not a salvageable item.
You should carefully box up all of the locomotives and cars. Many owners keep the original boxes, so you might find those under the layout. Otherwise pack them as safely as possible to avoid and damage to fragile parts.
Buildings, trees, and other loose scenery items should be stored separately to avoid damage and to keep loose material (ground covering, etc) from getting into the locomotive mechanisms. If the buildings are lit, cut the wires as far away from the building as possible so the next owner has plenty of wire to connect everything up again.
As for the trackwork, switches are the best thing to salvage, as they are often not glued down as securely because of the moving parts. If the trackwork is securely fastened down, it is most likely a loss too. As for electronics, homemade switch panels probably aren't worth much, but if this layout had a modern control system such as a Digitrax or NCE DCC system, that is worth saving.