Hey JWolf
Sorry for the confusion, that is because gold gain is account bound, since you've already beaten those scenario previously. Normal and Heroics do not gain gold after you have already completed it. Only Legendary difficulty grants gold every time.
As long as you are connected to PlayFab, at the end of every turn, the game auto saves to the cloud. So if you wanted to change to another device for example, just make sure to complete a turn before switching over.
ArchSenex is correct, any purchases you have made with either gold or real money is stored to your account, so those can never be lost not matter what happens.