I mean Rocket League is game focused on matchmaking through an online platform. Its main game types will stop working when that platform goes away. That's just the kind of game it is, its not like playing Lego Star Wars at all.

I see playing a game like Rocket League more in lines of having a membership to club to play a certain game rather than owning a copy of the game to play alone, forever. The club will eventually go away, that's just the nature of such things.

I do agree its a good lesson to teach your kids about the limits and issues of digital "ownership" though.