I think one thing we do need to realize is that it's going to be very tough to find a good backup PG. First, there aren't a lot of good backups to begin with. Second, no up and coming player is going to want to backup Rondo, where he'll get little playing time and no chance of ever winning the starting job.
Because of that, our best bet is likely to explore a combo guard backup who could get some PT at the 2 or a wiley vet looking for a ring who would be content with 10 mpg.
But, while I don't think Robinson is the world's greatest fit here (for us and him), he's probably better than most other options.