If Jones went down, I don't see why McCluster would split touches with Charles; McCluster an outside runner that frankly doesn't run as well outside as Charles does (then again, nobody does, with the exception of Chris Johnson.) He would probably see an increase on 3rd down action, so maybe 3 touches a game more than he gets right now.
If Charles went down, however, it is possible McCluster could see 8-12 carries and 5-7 targets. Charles is the Chief's biggest weapon, and though McCluster cannot replace Charles, there are things Charles does that McCluster can do a lot better than Jones (screens, draws, sweeps, flat routes.)
Short answer: McCluster could see a significant increase in touches if Charles was injured. If Jones is injured, McCluster would gain maybe 3 touches a game.