For sure 100% people are still gonna be using it though in smaller scale. It's undeniable that majority of usage is always for investment though bitcoin is also good for payment.
If government somehow out of the blue announce to outlaw BTC, people will sell it and price plummets, but guess what, it won't be completely dead, I'd even say it's still gonna be frequently used, the blockchain would still have many transactions.
The biggest downside is just the price going down. But that's about it, we're used to bitcoin at sub 1k anyway. However, there's really slim chance bitcoin gonna be outlawed.
But is it really worth the risk? I mean, most people would be afraid of getting caught by the government. They could either face fines, jail time, or worse-case scenario, death. With market prices going all the way down the drain in an instant, almost no one would use BTC or altcoins. It's has always been about the money.
Why would it not be? People take stupid risks for all sorts of useless or even personally damaging behavior. Bitcoin is freedom and nothing comes even close to it. How much would you risk for freedom if not everything?