Calendar split between local and iCloud -> merge?

I have a bunch of calendars after importing from Outlook but they are split between local and iCloud. I have a few questions:

1. How do I merge them together?
2. If they are all in the cloud will I lose them if iCloud is unavailable or disappears? Basically will my Mac maintain a local copy anyway?
3. If they are all merged to local will they then not be available to my other devices?

Thanks in advance.