What are the risks of social isolation?
Social isolation can lead to feeling of loneliness that can cause depression and other mental health issues. It could also lead to social anxiety, when the individual does go out and interact with people.  
I read a research that show that the magnitude of risk presented by social isolation is very similar in magnitude to that of obesity, smoking, lack of access to care and physical activity.
My suggestion to those who are socially isolated will be to try to get yourself out of your comfort zone. Go to meetup.com to find people who like to do similar activities like you and join them. Once you are with them, reach out and introduce yourself. If all else fails, speak to a therapist who can provide activities to help you out.
Mental health is super important so take care of yourself and your loved one.