Banishing all cards in your hand/on your field is the cost, which must be paid upon the cards activation. Cards cannot be chained until the cost is paid. So, chaining Mystical Refpanel would just give your opponent two cards and you would banish everything.
Same way activating Dark Bribe in response to Solemn Warning wouldn't give your opponent back their 2000 they paid. They had to pay it to activate, even though the card is negated.
Clever though. The more subtle rulings are always what get ya.