Just be calm and keep your alts if you bought new or are still holding. Never sell at a time when people are capitulating their altcoins. Do the opposite of others like I said very often. If you have listened to me in the past you sold Bitcoin at the top at $10000 in February 2k18 and bought the bottom at $3500.
And yes, alts can still drop another 30-40% from here, we don't know. But they will grow even faster after that. Don't make the same mistake like in the past. Fomo will let you losing your money!