You'd probably want for a try catch: Try catch (0) Instant Split Second Exile a card from your hand. You may cast a card from your hand with CMC greater than o

You'd probably want for a try catch: Try catch (0) Instant Split Second Exile a card from your hand. You may cast a card from your hand with CMC greater than or equal to the exiled card as though it had flash. That spell gains "if this spell is countered, you may play the exiled card without paying it's cost". ... Of course, it's not perfect but it's closer. Doing things like "reset the game state" are not defined in the rules very well, especially since the state wouldn't be the same (there are ways to make it illegal to undo). So that would just be a mess.