To everyone who lost or think they lost their MC Dungeons character, I may be of help. Caveat: I just started playing this game a week ago so I don't know how many times this game got updated, so this is my suggestion as of today.
This is where your character gets saved.
C:\Users(your name)\Saved games\Mojang Studios\Dungeons(lengthy numeric folder)\Characters
Open this folder and your character is the dat file. Pay attention to the date time stamp. That was when you last played the game.
If you uninstalled and reinstalled the game, you may have two or more (lengthy numeric folder). Depending on how many times you uninstalled and reinstalled the game. This is where your character is saved. Compare the date time stamp and size of the dat files in each of those folders. Move the older dat file to the newer folder because the reinstall created a link to that new folder. Restart the game and you should see your old character come back to life with all your loot and even stuff you may have left with the Blacksmith. Make sure you select switch character and browse through each one.
Optional: You can actually rename the dat file to something easier to remember such as an actual Character name. For example, Slash or Fluffy Dog. Try it. Make a copy of the file and paste it back in with the new name. When you open up MC Dungeons again, select switch character and you will see an exact same clone. The difference between this and making a clone from the game is that you keep all your Emeralds and entire inventory!
I hope this helped some of you.