Are you sure it's the disk group that's disabled and not the volume?
If you type vxdg list, what does it say in the STATE column?
Normally a volume will not be disabled by a failing disk unless it is in great jeopardy, i.e. if both plexes (mirrors) of the volume are damaged, etc.
Do you have a replacement disk?
If you type vxprint -v, are all or any of your volumes enabled?
Questions, questions, always questions...
Annihilannic.