This depends on each casino and the game you were playing.
Often for roulette, if you lose connection before the spin takes place then your bets will be returned to you – although not always. If you are halfway through a hand on blackjack, you may be given the opportunity to complete the round on a temporary table once your connection resumes.
Be sure to check each casino’s terms and conditions or FAQs to understand what happens if you lose connection. Alternatively, contact their customer support.