Hi, thank you for contacting JustAnswer.com. My name is Russell. I will do my best to provide the right answer to your question.
I would like to help - I appreciate that it sounds like a difficult situation.
The question I have to ask about the task is, what accounts are they? i.e. are they online accounts with online websites?
Or other accounts, such as Windows login accounts?
If the web browser program he used stores passwords, then auto-fill of those stored passwords may help access some of them.
And please note at this stage: you have to have the password, and access them, to close them. A 'merge' of online accounts with the same provider e.g. Hotmail, or Facebook, is something very dubious in my opinion, and many of them will have to be closed, I suspect. But it may depend on the specific website and its policies and capabilities. Certainly ability to login is needed, to prove ownership / proprietorship of the account.