Its probably a tumor and its probably very fast growing, so I don't know if that indicates a long life for the chicken.
if you're up for it, see what it is; in the best case sceneario its just a benign growth and youve gotten it off....it may be vascularized but its unlikely that it would be a main artery or some such.
You can tie it off from the outside tightly around the tumor with waxed dental floss in a slipknot, if you can get around it, then incise the skin to see what it is. if it starts bleeding
pull the floss tighter.
you can use styptic powder or baby powder for bleeding, but if its tied off it shouldn't bleed out.
Any vascularization of the tumor is not the main feed to the foot, its an offshoot...so while you want to be sure that it doesn't empty all the blood from the body
its not gonna be like cutting the jugular or something.
Ive done alot of bumblefoot surgery over the sink and while there is much more bleeding than I ever envisioned, it stopped, clotted and healed up very well.
Ive seen descriptions and pics of stomach and crop surgeries here where its the same....there is some blood, and its good to have lots of paper towels or a sink to let it pour into
but its unlikely that it wont stop bleeding.
I hope you put up pics of the thing...its educational for those of us who like the medical aspect of life;-)