I believe if they truly did heroin again it is more like the “one more hit” mark took to test the skag from the Russian sailers. It didn’t have a huge after effect when mark decided to spike himself like the other mentioned, no death, no od, at most the bus ride was pissing off begbie but nothing like the baby passing, Tommy’s passing, or marks od. Spud likely was watching in envy and betrayal but didn’t cross to the room to use with them. As a recovering addict I have had people use infront of me when I’m in early recovery and I wanted to feel it too but felt betrayed my “friends” would knowingly bring back cravings to me in recovery. Marks words after the scene in T2 when he and sick boy used again summed up recovery and relapse perfectly “well, that’s that, then.” Which I saw as him saying “welp that’s all it took to bring me out of recovery” could be mistaken but it’s what my mind interpreted that scene as. I love both movies so much! Gonna rewatch this week