When an Ubuntu release goes End-Of-Life, a few things happen:
1. The repositories move from archive.ubuntu.com to old-releases.ubuntu.com (so you need to edit your /etc/apt/sources.list to the new address)
2. These repos stop being updated--no bug fixes, no security patches, nothing (but you can get new apps from PPAs or from source, as always)
3. Third-party developers stop supporting the release (no more 8.10 intrepid downloads at virtualbox.org for example) and quality and quantity of support decreases at places like ubuntuforums.org
What is the absolute worst-case scenario? As always:
CrunchBang Linux is not recommended for anyone needing a stable system or anyone who is not comfortable running into occasional, even frequent breakage. CrunchBang Linux could possibly make your computer go CRUNCH! BANG! Therefore CrunchBang Linux comes with ABSOLUTELY NO WARRANTY, to the extent permitted by applicable law.