You may be able to get your number re-assigned however I cannot guarantee this as numbers, once no longer active, go into a state of quarantine (so that the number is not assigned again for a certain timeframe). The only way to get this arranged (if possible) is to speak to Boost. As you are overseas I suggest that you contact Boost via live chat (24hrs, 7 days)
If they can reactive your service with the same number you will likely have to purchase a Blank SIM and they will reactivate the service with the old number. If they can get the number reconnected, I would also advise you double check to make sure auto recharge is set up to avoid this issue in the future.