Is a double mastectomy worth it for an 11-year-old dog with a tumor?

Unfortunately, this is a difficult situation because most tumors that are cancerous and rupture are not going to heal on their own. A double mastectomy will be a very large and could be difficult recovery time for an 11 year old dog. Also, please know that even with surgery, you may not get another 3 years out of her simply because she is already at the top end of her life span. Also, there is always the risk that the cancer has already spread. Another option you may want to talk to your vet about is whether they can just do a palliative "debulking" of the mass that has ruptured. If there is a way to just resect the one tumor that has ruptured, this potentially could give her a good quality of life without doing a full double mastectomy. With the tumor being ruptured, I am afraid you are being forced to either do a debulking surgery, full mastectomy, or euthanasia. Leaving it alone isn't a good option because it won't likely heal on its own and if it isn't already, it will become infected.