The original design must remain, and amusingly, that means including some accidental errors from the game's very first print run
If at least one target is still legal, the spell or ability does as much as it can to the remaining legal targets, and its other effects still happen
Cards like this are great for two reasons
You can also drop Hexdrinker on a later turn and immediately level it up to at least the "protection from Instants" level, which will protect it from Erode, Doom Blade, Lightning Bolt, and Fatal Push
We won't be able to win in one turn, but this wasn't happening very often already, but gaining 10 at a time is perfectly reasonable