>>514074686 (OP)
As long as the Sentinelese exist, there is a risk that their genes will eventually be introduced into the wider world's gene pool.
If that happens, their genes would proliferate rapidly because the Sentinelese are extremely r on the r-K evolutionary spectrum. That means that their reproduction rate is naturally very high.
This proliferation would exert downward pressure on humanity's intelligence and upward pressure on its psychopathy (meaning that people would have less conscience).
The Sentinelese's innate tendency to quickly multiply is currently masked by their primitiveness and small geography. But those constraints would be lifted if their genes made their way into a modern world of illegal immigration, welfare programs, aid from white countries, etc.
Book on the r-K spectrum in humans (downloadable PDF):
https://philipperushton.net/wp-content/uploads/2017/02/Race-Evolution-and-Behavior-ocr.pdf