Varanids: efficient respiration in comparison to other squamates, intelligent, adaptable, likely to survive another mass extinction. If a mass extinction happens, monitors are one of the more likely candidates for dominance of terrestrial niches.
Crocodilians: not as likely as Varanids due to larger size, but size could also boost it on it's way to niche dominance. Ectotherms and capable of hibernation so lower energy demands than endothermic mammals.
Aves: inflexible body design; unlikely for wings to revert to arms, as seen in ratites. However, adaptability and quite a few intelligent species mean it has relatively high survival chance.
DId I miss any?