No, but he can request a 12-month extension from the JSIS given that he will still be a student.
Like the JSIS, only children recognised as disabled, can remain covered beyond 26 years of age.
After 26 (apart from the said 12 months), to replace the JSIS and any complementary health scheme, the child should join a national health scheme in their country of residence, such as a mutuelle or a complete policy with DKV or Partana, etc).