In order for you to show the offline user in Chat.
Step 1:
Login to CometChat admin panel.
Step 2:
From Left Menu Click on "Settings->General"
Step 3:
Search for "One-on-one Chat" section.
Step 4:
In this section search for "Hide offline users in Contacts Chats?" to "No".
Step 5:
Click on "Update".
Step 6:
"Clear Cache" from the Admin Panel.
Step 7:
Clear Cache from the browser.