We know that sandworms are territorial and control an area up to 400 km2.
Paul leaned forward, touched Kynes’ shoulder. “How big an area does each worm stake out?”
Kynes frowned. The child kept asking adult questions.“That depends on the size of the worm.”
“What’s the variation?” the Duke asked.
“Big ones may control three or four hundred square kilometers. Small ones—” He broke off as the Duke kicked on the jet brakes.
From the Q&A What does the word "thumper" mean when used to measure distance?, we know that a worm can be ridden for approximately 500 km before being released.
At that point, the worm is tired, it's far from home, and possibly in the territory of another worm. In the Terminology of the Imperium, the entry for Shai-Hulud says (emphasis mine):
[...] Sandworms grow to enormous size (specimens longer than 400 metres have been seen in the deep desert) and live to great age unless slain by one of their fellows or drowned in water, which is poisonous to them.
So, is being summoned by the Fremen tantamount to a death sentence for a sandworm? Is there any evidence in any of the books that the worms return their home territory? Or that they carve out a new life, far from home, by ousting whatever worms happen to be where they are released?