Well, you could take a bus from Chengdu to Jiuzhaigou in Jan. However, the safest way is flying there directly although the road situation has been recovered mostly from the earthquake's damage. Well, the Jiuzhougou's scenery in winter is greatly different from it in spring. There should be another charming scenery when the whole valley is covered in snow. Here is a picture of Jiuzhaigou winter: http://www.mjjq.com/pic/20081112/20081112022321482.jpg

The road had been already fixed and the problem is it maybe cold to be there in Jan. Generally, it is safe. It is 10 hours to go by bus. Or you can choose to fly to JIuzhaigou from Chengdu. Keep warm. You may miss the most beautiful scenery of Jiuzhaigou, but it has other kind of beauty in winter and it is not crowded at that time.