What happened shows that any user should withdraw their funds from the exchange after they've finished their trade.
I think that what happened is more an indication that people don't care and almost beg to lose funds. We have had so many examples of why people shouldn't leave any coins on an exchange, but they still continue doing it.
For what will happen to exchange is unpredictable. Cryptopia, even how
sh*t they are to other are way better compared to other mid-range exchanges around.
And besides, it's not about storing coins why we used these exchange. In my case, my altcoins there are only traded in Cryptopia with a good volume. Now to minimize the risks of being scammed should I trade it instead on DEX with dead volume? Of course no. Therefore I will use Cryptopia as I have no other choice compared to just idle my coins on a secured wallet and wait for it to become dead. I already got a decent profit playing from Cryptopia and for what happened to them is part of the risks.
Could you suggest me a wallet to contain all the altcoins, or at least the most possible please ?
There is no such thing as wallet that can stored all altcoins.
However, there are multi-cryptocurrency wallets. You can consider using:
a) Hardware wallets (Ledger, Trezor)
b) Coinomi
c) Exodus
d) MyEtherWallet for ERC20 tokens