Was there ever a coin that went completely to 0 and was abandoned in the TOP20?
As far as I can tell, the answer is no. But please correct me if I'm wrong.
Now, what if this never happened? There is every reason to assume that it doesn't really matter at what point you buy in for a specific currency. Just wait long enough and there will always come a moment in time that the value of the coin you bought is higher than the moment you acquired it.