One thing most people don't know about Two-bit is that he had something wrong with his heart. He had to go into surgery right when he was born and has a long surgery scar on his chest. The gang knew he'd need a transplant to make it past 25. Right before Joynny died, Johnny checked to see if he had the same blood type as Two-but so if he died he'd donate his heart. Unfortunately, their blood types were uncompattable. 

A week later, an official looking woman came looking for Two.

"Who are you?" He asked.

"I'm  Amy Green. Dallas Winston's social worker." She said. 

It turned out that Dallas knew he'd probably die young like he did, so he filled out forms so that if abc when he did, Two-bit would get his heart.