As he is leaving Johnny Cade's room in the hospital, Ponyboy Curtis meets Two-Bit Mathews, who is bringing a copy of Gone With the Wind to Johnny; Johnny had requested the book. Both Two-Bit and Ponyboy realize that Johnny is probably dying.
Two-Bit stood and looked at the door a long time. "I wish it was any one of us except Johnny," he said, and his voice was seriuos for once. "We could get along without anyone but Johnny."
Johnny Cade was a common bond for the members of the "gang"; each of the boys loved Johnny and did his best to protect Johnny from his parents, as well as anyone who intended to do him harm. Johnny brought out the best, softest side of each young man, especially Dallas Winston ("Dally"). According to Ponyboy's narrative, Johnny "was the gang's pet, everyone's kid brother." It would probably be safe to say that the gang felt that as long as Johnny was safe, so were they; they needed someone to protect and if they cannot protect someone who so deserves to be safe, then there is little hope for them.
As mentioned in the book a lot Johnny was the one that brings everyone together. Making everyone happy, and he is also the, 'pet' of the gang.