The loss of someone in your life can often leave family dynamics with missing pieces, as well as friendships, work environments, etc. As if experiencing the loss of someone you know is not hard enough - after that person is gone there can be the question of who will take on the responsibilities they once held. This can come in many forms. Some examples of this would be if a family lost their father and it left them in a single parent household with no adult male influence - this could cause a young boy or even a teenager to act as though he is the "man of the house." Another example is if a group of friends loses someone, someone might feel as if they have to take on that person's "role" in the friendship circle.
Of course, no one will ever be able to take that person's place in our lives and in our hearts. But, it is normal to feel like taking on parts of their role or their responsibilities might help fill the void of their absence. There is nothing wrong with helping out by trying to take on a new role and step in where that person once was. However, if you are the one doing this, do it gently. Others might feel threatened as if you are trying to take the place of their loved one. People often need help after the loss of a loved one - not just emotional support, but actually having someone around to help with chores, responsibilities, etc.
Just remember - if you are someone who is experiencing grief and loss and you need an extra hand - do not be afraid to ask. You might be surprised who is willing to help you out. Also, never feel bad that you are looking elsewhere for the things that your loved one once did for you. I imagine they would want you to have the help and support you need.
If you are someone who is providing this extra help for an individual or family, just remember to be patient with them as they are grieving (and you probably are too if you knew the deceased).