False premise. My guess is either steam won't refund you OR they would take back the cards (or money from selling them etc). Either way I don't think you'd have any chance of getting a 2nd set of drops.

I've actually had a friend refund a game and repurchase it, so I interrogated them about it at the time.

What happens is that your "card drops" for a game is static. If you refund/rebuy a game, steam remembers what it was on before.

So for example, if you bought CSGO (3 free drops) and idled it for 2, then refunded it because holy crap it's on 1 hr 50 mins, you'd have the 2 cards still. If you then bought CSGO again, you'd now have 1 drop remaining.

Equally if you had all 3 drops gained, you'd buy the game and have 0 drops.

As a side-note this "plot" will work exactly once in your account's lifetime, as upon refunding a game for the first time steam stops giving you card drops before the 2-hour mark. So you may wish to avoid getting refunds unless you want to have to play every single card game of yours for 2 hours to gain a bunch of cards worth 4c.