Answer 2 ) Have your dad to contact US embassy Kathmandu. They will give him a form to fill up and need to pay around NRP 20,000 fee. The form is to reinstate the GC. Your dad has to mention the valid reason ( medical is the best option i think) to stay in Nepal for long time. Either Your dad can come back in USA if they approve it or they will deny it. Then you have file new i-130 for him.