You have to check your insurance contract. Most do not preclude dependents attending a military academy (just like a normal college student who elects school medical insurance) but they most probably become secondary payee under most dependent provisions after TRICARE kicks in. Just like when MEDICARE kicks in everyone else bails to second or third even if you have been covered for forty years. It always comes down to a cost benefit analysis. If it doesn't cost more to let them remain on the coverage, keep it. My Mid is still listed as a dependant on my Wife's policy as there was no additional cost. I dropped her from mine since it would have cost $200 a month to keep her on with no monetary advantage after calculating deductible and balances due.