Service Master Key inaccessible, SSRS key only one backed up
For anyone who comes across this and has a similar issue...  

I was able to successfully change the SQL Server Service login to the original account used when the service master key was created, then successfully back up the key.  Therefore I did not need to regenerate the service master key and restore the SSRS key.  I still don't have an answer - if the saved SSRS key could have been restored following the service master key regeneration.

If anyone learns the answer to that - when you have backups of secondary keys, but not the service master key - will you have to regenerate the secondary keys also, or be able to use your backups.... please post the answer here for future reference.