After five blissful years together, Mogwai's cagemate Gromit recently passed away suddenly. It was obvious he missed him terribly. My usually hyperboy was depressed. He'd go looking (4-level cage) for his buddy and was upset when he couldn't find him. He did eat and play, but without gusto. He was miserable and lethargic. I was really concerned he would literally grieve to death (as happened with my hedgies two years ago).
I adopted two beautiful 4-month old brothers. They had a health check from the vet before they came (and came from a loving breeder). I decided on a semi-quarantine -- kept them in another cage (not with Mogwai) but in the same room where he could still see them.
I will add I believe in total quarantine but under the circumstances it would not have worked if he died from loneliness during the quarantine!!! Sometimes you have to follow your gut/mommy instinct.
Mogwai perked up immediately. He made one last superfast pass through his cage to look for Gromit, but has been okay since. He is back to his old self. He takes his toys and hay cubes to sit in the corner nearest the babies and play while watching them. There is no doubt in my mind they most likely saved his life, or at least improved the quality of it. He had never been alone before, and I don't look much like a chin. Would he have gotten used to being alone, -- well it wasn't worth the chance to me.
After more time has passed, I will carefully do intros. But even if it doesn't work, and they have to stay in separate cages, I know now he will be okay just seeing the other chinnies around.
I totally vote for a new friend for your chinnie. No matter how much human attention we give, it isn't the same.
The new boys are Gremlin and Gizmo~