From the Classical period and onwards was sonata form substituted by other forms as basis for most instrumental music?

Sonata form remained a foundational principle for most instrumental music well beyond the Classical period and into the subsequent Romantic and Modern eras.

Composers from later periods continued to utilize and extend the formal conventions established in sonata form, evolving new variations and departures while preserving its underlying structures. While some composers ventured into alternative structures and modes of development, sonata form persisted as a prominent compositional concept that retained much of its influence.