That comparison doesn't work here I'm afraid. rune pages are not cars, they don't expire, they are permanent systems, and yes you should get 100% refunded for it. let me break down my reasons why.
2 Players have 15,000 ip. 1 player buys 2champs, the other player buys 10 runes.... ok now here me out..
If riot then decides to remove any one of those things from the game, the player who made a different decision will be s*** out of luck.
But image that instead of that, riot gave a trail period for both systems, for 3000 ip more, you can either rent a champion for 7 days, or rent runes for 7days.
If riot decides to refund 100% of the cost to the person who rented the system, and only 30% of the cost to the person who spent full money on the system .... don't you think that is a bit f-ed up? Its essentially like saying ( using your car annology ).
"Hey you know that $30,000 car you spent your life savings on? well turns out there was a manufacturing issue and we gonna have to recall it, but since you already used it, were gonna have to pay you back $5,000 instead. But you know that other guy... the one that rented it for $12,000 instead... well even though he drove it way more than you did, he gets full refund because it was just rented. sorry just business friend"
Now if a manufacture actually did this, you could actually sue them unfair business practices. But riot is not a care company, they don't actually loose money for this ( as far as I am aware ), so it doesn't seem to be any reason why longer vetertan players get less than players who only recently started buying runes.. Getting less for using something more doesn't make sense. Your not selling runes, it is being taken away from you. And while riot has full rights to do so, why would compensation change based on when you used it??? that part doesn't make any sense