All depends on the quality of the coin. And if the coin is already in the top rankings, I think it will be safe and not return to zero.

Which I have experienced so far that many coins to zero because it has poor quality. These coins are hard to find buyers. If the Altcoin season comes back, all the coins have the potential to grow bigger. So with the dominance of Bitcoin is now better focused on Bitcoin, and hold your Altcoin.