He's cheap insurance if there's an injury to one of the established rotation guards. There are no plans to use him this season without an injury.
At the same time, though, they are watching him in practice. If they like what they see in practice, he'll get signed for next season. They do want more reliable shooting going forward. I do believe they are willing to see if Jimmer could fill that need.
All that said, Thibbs is not down 2-0, having lost both at home. He's got nothing to lose at this point, and the established rotation isn't getting it done. Might as well see what could happen.