How safe is BSC (bep20) chain? Is it okay to store a large amount of BTC and USDT on that chain? If Binance shutdown will the chain still operate normally?
It isn't safe at all to store even very small amount of BTC on BSC because frankly speaking you can't store BTC on that. BTC is stored only on Bitcoin's own blockchain not any other blockchain. The one which you're talking about isn't BTC at all, it's just another altcoin pegged to BTC's price. You should purchase Bitcoin only if it's on Bitcoin's network and blockchain, not those altcoins.