Hey Max,
Deleting users is not implemented right now. I've been running under the assumption that if you use Kviklet seriously you set up SSO and deleting the user in the SSO provider will prevent them from logging in. Which should usually be enough.

The problem with deleting the user is that comments, reviews and requests are attached to the user profile so deleting the author would mess with the auditlog and leave orphaned requests.
If you have password logins, it probably makes sense to simply remove all permissions from this user for now.

I will think about a solution where you can mark a user as disabled, preventing them from taking any action in the future but preserving requests, comments and reviews for auditing purposes.