Is there a way when a save to repository task is suspended to re-assign back to a user?
Is this an option as a feature in the future to be able to step the process back one step if something goes wrong?
No, once an instance has made it to a Save to Repository step, it can't be reassigned back to a user.
Is the problem that the repository requires a field that the form filler didn't fill out? Or that a value doesn't meet some requirement for the metadata field? In these cases, you should design your form with required fields that map to required metadata fields, or put similar restrictions on your form fields to match the metadata fields. If you find forms are still getting through with bad values, you can always add a gateway to programatically check for bad values and route them back to the user task if it catches anything, or a review user task to manually check for any errors.
Best thing to do is read the reason for the suspension and fix that.
You will see something ugly when viewing the error list it looks like:
"Another operation on which this field depends failed [9087]" (Kind of looks like this)
And you will see in this list, the bunch of errors have a dissimilar error, this error will be the reason for the suspension.
Also what Jared said above is pretty important. Designing forms properly is something I wish I knew how to do from day 1.
Good luck!