The second line currently isn't the reason we're winning games. Backlund has looked quite slow in the last few games, and if there's already a decisions that he's going to miss time, it could easily be a Monahan situation where this is simply a good excuse for the Flames to let him get finally healthy from some pre-existing injury.
But on topic, the Flames' second line isn't currently the reason we're winning games. We have some leeway here to experiment with things a bit. I don't think it would be a bad idea to try Bennett at second line centre there, at least to start with. Throw a right winger with Bennett and Tkachuk and let's give them a chance to prove what they can do. If not, we have options. Jankowski has been looking strong lately, and at the very least can be trusted not to be a defensive liability while on the shutdown line. Ryan could do it, but I don't trust him to take tough matchups. Czarnik maybe, but I don't know if he could handle those matchups either.
That's about the order of things I'd try. I think you want to break up the top line right now only as a last resort.