I sometimes buy balloons for my grandson when we go to WDW. Now that he is getting older he wants Star Tours instead of balloons.
But if you are flying you can slowly open the balloon by pushing a straw up the one way valve and letting out all the helium, then pull the straw out. then fold or roll the balloon and bring it home.
When you get home bring the balloon to Party City or Dollar store and have them refill it. They usually charge $2.00. Bring some colored Duct tape to put on the end of the balloon because sometimes the valve will leak after opening it. They always tell me they won't promise that the ballon will fill, but I have never had a problem. But if you do they can't replace it. I bought Birthday balloons once for him via mail order that were personalized and 2 of the 10 did not fill at the Dollar Store.
I had a mylar Mickey,Minnie balloon for almost 2 years until he finally wanted to get rid of it.