If so, build another server with the latest Carbonio-CE.  Use Ubuntu as then you can always integrate CBPlus's 2FA at a later date and it's fairly cheap.

I'm starting to do this myself.  The CBPlus package does include a free tier which has cool features but 2FA is not one of them and is only included in the fee tier.

Recreate all accounts, distro lists, aliases etc... on your new server.

Then attempt an imapsync to transfer emails from your crippled Zimbra-OSE install to the new shiny Carbonio-CE install.

I'm uncertain if the DB being down will prevent imapsync from working but try it. 

This happens a lot with the scripted installation; it's really annoying; it took me a while to work out how to get around it. 

run these as root; you basically need to completely delete all of the previously configured stuff. 

systemctl stop service-discover
rm -f /etc/zextras/service-discover/config.json
rm -f /etc/zextras/service-discover/main.json
rm -f /etc/zextras/service-discover/cluster-credentials.tar.gpg
rm -f /var/lib/service-discover/password
rm -f /var/lib/service-discover/*.pem
rm -rf /var/lib/service-discover/data
mkdir -p /var/lib/service-discover/data
chown -R service-discover:service-discover /var/lib/service-discover

Followed by 

# Type a strong password when prompted (it will not echo)
read -s -p "Insert Mesh Password: " MESH_SECRET
echo

# Confirm it is not empty
echo "Password length: ${#MESH_SECRET}"

# Run the first-instance setup
service-discover setup $(hostname -i) --first-instance --password="$MESH_SECRET"

hostname -i should yield your IP address; alternatively - you can hard-code your IP address with 

service-discover setup xx.xxx.xxx.xxx --first-instance --password="$MESH_SECRET"

if this fails - you can try 

service-discover setup-wizard

 /etc/zextras/service-discover/cluster-credentials.tar.gpg <= this is for multi-server environments which is why on a single server installation it is missing... 

(1) fail2ban - are you using this? 

If so, check /etc/fail2ban/jail.conf

Make sure the host's IP address is within the range:- 

ignoreip = 127.0.0.1/8 ::1 39.80.9.0/24

(2) Check Carbonio global config settings 

su zextras 
carbonio prov getAllConfig

getAllConfig will output all of the global config; I happened to have changed the host name and IP address of my server and got the error; and I found out that the hostname and IP addresses are hardcoded into the configuration when you do the install. 

These are the variables I ended up having to change:- 

carbonio prov modifyConfig +zimbraMailTrustedIP 39.80.9.197
carbonio prov modifyConfig +zimbraHttpThrottleSafeIPs 39.80.9.197
carbonio prov modifyConfig zimbraReverseProxyUpstreamEwsServers new.hostname.com
carbonio prov modifyConfig zimbraReverseProxyAvailableLookupTargets new.hostname.com

you can do a 

carbonio prov getAllConfig | grep old.hostname.com
carbonio prov getAllConfig | grep old.ip.address

After that you will need to restart the proxy server + appserver - if you are running the latest versions of carbonio (26+); I think the commands are to use systemctl. 

systemctl restart carbonio-proxy.target
systemctl restart carbonio-appserver.service
systemctl restart carbonio-mailthreat
systemctl restart carbonio-nginx.service 

(3) Go to the file /opt/zextras/conf/localconfig.xml 

And search for old hostnames and old ip addresses - make sure these are up to date 

(4) Check /etc/hosts to make sure that the hostname points to correct ip addresses

(5) Any firewall like csf or fail2ban has

127.78.0.0/24

127.0.0.0/24

as allowed - because carbonio uses these internal addresses for things. 

The server is basically a home system running in what should be my bedroom lol.... I got the coach as a result haha.... but yeah it started many years ago as I am neuro divergent with both autism and adhd and found it difficult to be in employ and work with other people, so I decided to build my own stuff as that was where my interests lay....

Sadly after so much time my health is really struggling now due to severe "autistic burnout"... I scored 100% on an online test and can barely perform higher level tasks. 

That's why I am eager to find out if there is a supportive and vibrant community that could help me doing stuff if I get stuck which maybe more often now then previously when I was still completely capable.

As long the documentation is good I should be able to follow it but if there are any hiccups along the way at least I can turn somewhere and not loose everything.

Currently on Zimbra forums right now trying to recover the DB.... 

I came over to Carbonio as I've known about it for years and since Zimbra went "closed source" in terms of no more web UI etc... so I thought it might be a great option to move across to as an active project??

Though my health has been dwindling for the last 3 years I even considered just using Gmail and pointing my domains to that but I'm not sure if I want the extra expense of constant payments.