I'm sorry to hear about Rags, dbg10
We've had a dog with hemangiosarcoma--we had a positive diagnosis because the cancer had spread to his lungs.
I'm not sure they can tell from just blood work weather it's a hemangiosarcoma or a benign hemangioma, though.
Either condition leads to blood loss through internal bleeding, though. Our dog never showed any discomfort from the condition, although because of the lung involvement, his breathing was impacted his last couple of days. But the primary tumor didn't seem to cause him pain.
Because he's anemic, Rags might feel tired, but anemia isn't usually a painful condition, either.
It's been some years since we had experience with hemangiosarcoma. Maybe there are different treatments now, but back then the only treatment option was surgery to remove the primary tumor before it burst and bled out.
If the surgery is successful and the tumor proved to be a hemangioma, then the dog was 'cured'. If it was hemangiosarcoma, it would likely recur somewhere else in the body.
What terrible timing for you, right before the holidays
Whatever you decide, you're in my thoughts and prayers, dbg10!