If Tua is going to miss significant time but plans on returning, you have to find a veteran that can fill a gap for the next month plus. If you think that Tua may be looking at calling it a career (which is not likely, but still could happen), then I think it would make sense to bring in a guy that has a chance of turning into a QB of the future. In that case Zach could be an option, as would Trey Lance and maybe even Tyler Huntley (who has looked pretty decent in limited opportunities).