He just walks away and that's it? No information on him? Because there seems to be a lot of info on everyone else attached to Billy the Kid (Rudabaugh, Chavez, Scurlock, Bowdre, O'Folliard, Garrett).
I'm not really sure but if you listen throughout the movie nobody really knew that he rode with Billy and he left before anyone really got a chance to know who he was. That's be best theory I got.
"I'm Gonna Kill You All Kinds of Dead" - The Spirit
I'm not 100% sure so take my word as gospel but I am pretty sure that Henry William French is a combo of all the other guys that rode with the Regulators. Bowdre, Skurlock, Chavez, Brewster, Rudabaugh, O'Folliard were the main guys I guess but there was actually like 30-40 of them and I think French is a composite of all the rest. There wasn't an actual Henry William French.
Hendry William French is based on Jim William French in real life. He wasn't scouted to ride with Billy when he was on the run. He was actually a Regulator, so he should have been in the first movie as well.
I just took it as he was the lone survivor of the movie. The irony being that he was probably the least likely to survive based on the fact that he had no experience was timid and clumsy. Yet he was the lone survivor.
Various reports indicate that he was shot and killed in a botched robbery in 1879. A year after the Lincoln County wars, which he was present for. He was involved in the McSween house battle as well as Buckshot Roberts outhouse shooting where Dick Brewer was killed.
The two movies take a lot of creative license with the real life characters. For instance, Doc's demise was really how Charlie Bowdre went out.