I think it won't be much different than in 2016. Obviously, there will be many people whose miners, now barely paying for the power they consume, will be losing money once the reward is halved. But that is also how things were back in 2016. Some then decided to pull out of the game altogether, others kept on running their miners either because they weren't the ones paying the power bills or because they were looking forward for the price to climb higher and to offset the losses.

If too many pull out of mining, the difficulty will recede, making mining profitable again for some, luring them back. And, depending on the jurisdiction and on how people declare their mining income, (if at all,) some may actually be able to claim their losses as a deduction from their taxable income.

So I don't think we can expect a "death spiral". I remember sharp drops in value back in late 2013, then in 2015, but Bitcoin did recover after that, breaking records in 2017. So I don't believe we have much to worry about when the halving takes place.