I suppose that depends on your RTO. With cloud providers, even on a bare VM, you can to some extent get away with having no IaC, since your data (and therefore config) is almost certainly on networked storage which is redundant by design. If an EC2 fails, or even if one of the drives in your EBS drive fails, it'll probably come back up as it was.

If it's your own hardware, if you don't have IaC of some kind – even something as crude as a shell script – then a failure may well mean you need to manually set everything up again.