I run Greyhawk campaigns, but right now one of the parties is in the Temple of Elemental Evil, 1e dungeon run in 3.5e rules. Anyhow, they are in Elemental Nodes, which are sort of like Demiplanes.
So a Dismissal spell has an 80% chance of sending someone to their home Plane, but to me the Prime Material Plane contains GH, FR, Basic’s Known World, 4e’s Nentir Vale, Pathfinde’s Golarion, etc.
NOW comes the FR question: If a character gets randomly dropped into FR, where specifically would you have them land?