As hard as it is to watch a chin be lonely after losing a cagemate, I feel that it's better to let them adjust to being alone for a bit, before trying out a new bud. New introductions are usually stressful - I figure it's not a good idea to add that to the stress of losing a cagemate. Like Jo Ann, I do think that chins have hearts, and that we should always remember that and care for them accordingly.
Single chins can be happy if you give them alot of attention - make time in your daily schedule for a regular playtime together, etc. Regard this time as a transitional time for your chin and then decide what you want to do in terms of introducing another. In general, I think chins are happier with a cagemate, but I do have one chin that much prefers being a singleton.
Lori