ForestWind   

Pam Johnson-Bennett's helpful article, Do Cats Grieve? is full of support on helping your Siberian cat heal after the loss of another pet. 

"Many people don’t realize animals grieve the loss of companions and family members. Even if companion cats had a hostile relationship, the surviving cat may still grieve the loss. There’s confusion about where the other cat has gone. The cat, regardless of whether they were close or not, had negotiated territories within the household and now the surviving cat has to figure out whether to risk crossing onto that cat’s turf."

https://www.catbehaviorassociates.com/do-cats-grieve/" target="_blank" rel="nofollow">Click here to learn what to look for, how to act, strategies to help calm and soothe your bereaved pet all the while grieving yourself. 

Pam's book, https://www.amazon.com/gp/product/0143119796/" target="_blank" rel="nofollow">Think Like a Cat  can be very helpful in understanding your Siberian cat.