Hashirama was revived through Edo Tensei at a young age, you are revived as you die. The only exception to this is Madara as Kabuto did something special with him. You can be 40 and still have a grandchild, and 40 years old is still fairly young to die by today's standards and when you look at the characters in the Narutoverse, its fairly young to. If he died young then he either died of disease or in combat, say he died in combat. There wouldn't be a single Shinobi alive that could even threaten him the slightest. So no normal Shinobi would be able to even fight him head on, I also doubt thousands of shinobis would be able to do it. If he died of disease then that doesn't really make sense if he was able to grow back vital organs. Since a disease is a damage to the organs of the body.
He could simply rip them out and grow new ones. By all logical standards, Hashirama died from disease and as I said if he was able to heal like Madara is now then he wouldn't be able to die of disease. So, Madara's healing doesn't come from Hashirama's Senjutsu, it comes from him being the Juubi's Jin.
Also, there have never been a theory if the orbs could heal or not because it doesn't make sense and its not needed as the Juubi's Jin can heal perfectly well on their own.