"With an S Crop election can a Schedule C be completed or is 1120S the only option?"

Corporations are their own entity. There is no Owner; your taxpayer is a shareholder-employee. We form corporations to gain the benefit of this separation from self, which is different than a Sole Proprietorship or Single-member LLC (both of which file Sched C). That separation needs to be respected. There's still time to make sure your taxpayer knows about their payroll requirements; we see a lot of errors regarding that part of corporation operation.