Complex sentence: There were, however, worries of insuring O'Toole for the six remaining films in the series, and he was ultimately replaced as Dumbledore by the Irish-born actor Michael Gambon.
Split into simpler sentences: There were, however, worries of insuring O'Toole for the six remaining films in the series. Harris was ultimately replaced as Dumbledore by the Irish-born actor Michael Gambon.