If Helios had notice that his cattle was gone then whoever killed his cattle would be killed by Helios. This was shown in the odessey when all of the odysseuss men dies because they ate the cattle.
sacred cattle of the Greek sun god ~Helios
The cattle of Helios do not breed. The cattle are immortal, handsome, wide-browed, and curved-horned. They are directly owned by the god Helios.
The Cattle of Helios lived on the island of Thrinacia, equated with modern day Sicily.
hyperion or Helios
They are the only cattle that can fly.
After Odysseus kills the Helios' cattle, he is not sure what to do. He realizes it was a mistake and shortly afterward they kill his crew.
The sun god's cattle.
Helios keeps his cattle on an island called Thrinacia. It is believed that the location of this island is where the modern island of Sicily is now.
They see Helios' cattle and want to steal some.
Odysseus' men were forbidden to slay and or eat the cattle of Helios' island.
They disobey Odysseus and eat the cattle while Odysseus is taking a nap.