I think there's probably 3 tiers that exist.
Tier 1 = The guys everyone's talking about (Mario and Lane) and the 1a/1b hopefuly hires
Tier 2 = The back up plans that make sense and would fit but not the splashy hire (Mark Stoops and Tom Herman)
Tier 3 = Totally random throw some sh*t at the wall and hope it sticks
At this point, if none of the T1 candidates come then I think the next realistic option is Mark Stoops. I can't imagine Stoops says no to coming here. Herman would be a nice 4th option but honestly this one would come out of left field so would require new AD to totally think outside of the box.
Beyond those 4 then I think you just have a bunch of whatevers. No immediate ties to the program. No one beating their door down to be their next HC. Just a hail mary and pray for the best. O'Brien, Matt Campbell, or a big name assistant like Lebby, Marcus, etc.
IMO Stoops would be the best option if no Mario or Lane. I think he could build a solid foundation here: he has shown he has some recruiting chops, has a solid defense, and has shown openness to offensive innovation in his most recent OC hire. Give him money and resources and I think winning the ACC Coastal becomes the norm along with 9-10 win seasons every year.