Some people when they grieve want solitude. They choose to grieve alone. We must respect the person that is grieving. However, if you notice the person is disconnecting completely, then it might be time to reach out to them.
“And let us consider one another in order to stir up love and good works, not forsaking the assembling of ourselves together, as is the manner of some, but exhorting one another, and so much the more as you see the Day approaching.” Hebrews 10:24-25