To unlock Resurrect hero in Ironman mode. First, you have to create a backup of the saved game folder. When your hero dies, exit the game and restore your saved game data. Now, you have to start Regedit and use the "Registry/Export Registry File" menu option to create a backup copy of your original registry. Only after that you can make the following changes to your registry:
[HKEY_CURRENT_USERSoftwareEnlightWarlords Battlecry III]
"LIMHK0_A"=dword:00000000
"LIMHK0_N"=dword:00000000
"LIMHK0_X"=dword:00000000
"LIMHK1_A"=dword:00000000
"LIMHK1_N"=dword:00000000
"LIMHK1_X"=dword:00000000