Yep - this has been discussed a number of times. Usually it’s either your scenario (no control over offsite destination availability) or “do backup when USB drive connection like CrashPlan did”.
So far the proposed (by me) option I like the best is basically:
- at scheduled run time if job has not COMPLETED within the previous X hours and destination is not available, then re-schedule job for Y minutes later UNLESS that puts it past next normal scheduled run time
However, implementing such a thing is beyond me at the moment. Perhaps a GitHub post with a bounty request might make it happen sooner…