Malkin/Crosby on the top line isn't much of a worry right now. The important thing is that the other lines continue to contribute offensively like they did on Thursday. The lines worked really well the other night and MT has to stick with them until things go sour. However all it takes is one bad night for the 2nd and 3rd lines and Therrien will probably switch them up again. Sometimes Malkin/Crosby can steal a win themselves, but it won't happen every night, especially when we get into teams with a lot of depth. That's why I don't see them staying together too long, but he has to keep it rolling for the moment.
Either way it was a great move by MT to get everybody going. Staal, Fedko, and others have more confidence now so that when they are reuinted with Crosby/Malkin they'll be ready.