frank hawk
To avoid bunch of complaints and time wasted for reversions that'll surely come as gamers are not famous for reading capabilities, add one step that is actually engaging the user's attention.
It's usually done with user input. Here it can be too. For example, you could add a popup that says "Type in the username of account that will be deleted" with the word "deleted" highlighted as much as possible.
Then you could also completely disable linking accounts that're let's say 30 levels lower than the account that will get replaced. No idea who would ever want to do that and lose the progression on the higher level account.