Only the owners and admin can deactivate accounts. This is controlled from the settings tab, manage members.
Even when a user's account is deactivated, the user’s blogs and wiki will be still be available for view.
If a deactivated user wants to reactivate his/her account using the same username, send an invitation to the same email address s/he used to login (or a SSO login) to your team's Kibela account. S/he will be able to publish blogs and wiki using the same username.
Note: new members cannot claim the same username as deactivated users.