I lost a Follower when I was forced to lose a follower doing some quest.
After I return from the quest, I get a note from a courier that my I have gained some money from an inheritance. (300 gold)
Turns out my follower died and left me some money.
How do I find the corpse, and how do I get the items I had given them back?
Which platform are you on?
There are many cheaty methods with the PC to find the corpse. But with a 360/PS3 version you are confined to trying to find the body:
If you can remember where you dismissed the follower, and where they live then you can estimate where they travelled to get back home. They will always travel via a road or path where possible, so look along the shortest road route from A to B.
If you have a quest target in their destination town, then travel to where you dismissed them and use clairvoyance to display the shortest path. Run along it.
If you are on the PC one method with the console is
player.moveto [actor/object ID]
console command to port you to the body. You can get the actor id by loading a save where te follower was with you, opening the console and clicking on them - write down the code.