Your entire flock carries the virus. But if it's leucosis and not Marek's, your flock can lead mostly normal and long lives once you accept the limitations. It would be a good idea if you were to send this dead chicken off to a lab to be tested for avian viruses to determine which it is.
After years of trying to hatch eggs from within my flock and going through the heart ache of high embryo mortality, I quit trying. The few chicks that did hatch mostly lasted less than one year before dying. I have only had two chickens hatched within my flock make it past the one year mark into middle age.
Another limitation I discovered recently is that the disease can be passed to store bought chicks brooded by a broody hen carrying the virus. Those chicks, three out of four chicks a nanny hen raised, died around seven months from leucosis. They had received a heavy dose of the hen's viral shed over the weeks they slept under her at night. I didn't know it at the time but she was also symptomatic, dying not long after she had finished raising the chicks.
But despite the virus, many in my flock live long healthy lives and live to a ripe old age.