Hi!
There isn't really much to go on here. A rig shouldn't just disappear from a scene.
Normally you'd expect the file to not open up again completely or give you some kind of Error upon opening up. Did anything like this happen when you opened the file?
Are you sure that you are opening the correct Scene? Sometimes the latest save file doesn't show up in recent files in Maya.
Was the Rig maybe referenced in from a local file and you are trying to open it up on a different machine?
Is there anything in the Scene besides the Rig that is still there?
Do you maybe have a recent save of the Scene you could fall back on?
Have a nice day
