So you molly-coddle Henao a bit, give him the Giro to aim at, since he's a better GC bet than Arroyo, and do all those stage races while Valverde's aiming at the Ardennes. Then you give Henao the middle bit of the season off before building him back up again for September. Valverde rides the Tour as leader; it's the GT least suited to Henao so that's no problem until Henao's a bit older anyway, and then and only then do you have a problem if both want to target the Vuelta.
You make it sound like Valverde will want to ride every single race on earth. I know the likes of Joaquím Rodríguez didn't get the chances they deserved as a teammate to Valverde, but the likes of Joaquím Rodríguez were also more established than Henao, who may be better served in the lower-pressure situation of having an established team leader. Then, once Henao is in the position that he's a threat to Valverde, Valverde will be older and possibly more mature, or certainly easier to say goodbye to. Right now, with the palmarès he has, you'd be crazy to cast him aside so that you could pick somebody totally unproven in Europe without at least trying to work both of them together.