If I buy several lottery tickets and then leave my account dormant for a long time, say at least 6 months, and my ticket wins the jackpot during that time.
Will anything happen to my prize money? Will the casino refund my money because I never claimed any of the rewards?
It depends on the platform you use and their Terms and Conditions like some platform have rule of banning or deleting account after a specific time of inactivity.
rules like these can be found on their T&C page or directly just ask in their support chat, and you can also ask that they provide the winning lottery amount after long time or not.
casinos in which i play on gives lottery winnings directly into my account instantly after winning a lottery.