Banks transfer is the proof that you got the money from your friend.
Until and unless bank notified via death certificate of the customer, the account still be active.
If at all bank notified about the death of the customer then the ownership of the account would be transferred to 'nominee' . The nominee would have all the access of the account in future. In case, if no nominee registered then the account would be closed and the accumulated money would be transferred to his successors ( according to succession certificate ).
Note - Even if the account is closed still the transaction record would be available with the branch any time.
It is absolute illegal from your side to try to know the information about the account whether it is active or frozen.
answering to the 4th question - you may hold the payment till you get status of the account.
You can discuss with me whatever may be your views.