Well! It would depend on the reason I lost them. I think if I lost my friends due to something I did I would probobly self reflect for a while. I don't make close friends with people that I think give up on others so easily, so whatever I would have done it must have been bad.
If it's something I wouldn't be able to change however or I resolved that what they left for was personal preference only, I would probobly just look for new friends.
... if you were referring if they all died suddenly in a freak accident, I would make angel instagram edits of them and make sure they feel loved even after death. Then probobly go to the friend store and buy some more. ♡