I can explain the method used by Blizzard in their campaigns, I mean importing hero between missions.
You need to use Game Cache:
You need to create a game cache using action "Game Cache - Create game cache" and specify the filename of cache.
Then, use action "Game Cache - Store Unit":
"Store Unit<your hero> as Label<for example "myhero"> of Category<for example "heroes"> in (Last created game cache)".
After that, save cache using action "Game Cache - Save game cache".
If you want to restore hero, create game cache (as above) using the same filename, and then use action "Game Cache - Restore Unit Facing Angle" or "Game Cache - Restore Unit Facing Point". Use the same label and category to point where your char is.
I don't know it would help/work, because i don't know much about game caches, but i saw this method in blizz campaign "DemoCampaign.w3n" (included with Warcraft 3 TFT - xxx\Warcraft III\Campaigns\") and i thought it could help you. If you are not sure, look at this demo campaign and see how this works.
GL!