Varis did not mourn Zenos' 'death' during the end of 4.0 and explicitly referred to him as a monster unfit for the throne. As of his dying words, he also stated that the burden of the throne was beyond Zenos. So it is highly unlikely that Varis would have named Zenos as his successor. There is, presumably, others in line for the throne - though I have a feeling that Zenos will seek to take the throne regardless of his supposed lack of interest in it as his new outfit in Dissidia NT is explicitly called 'Imperial Court Attire' which suggests to me that he is going to embrace a high ranking position within Garlemald so long as it serves his goals.

Which sets things up nicely for freeing Garlemald from Zenos' tyranny. Varis genuinely cared for his people yet in many ways his hands were tied by Ascian scheming. Zenos, however, cares nothing for his brethren and would likely exploit them if it meant achieving his goals. I think it's likely that Gaius and Estinien survive their confrontation with Zenos but they will likely have need of withdrawing and gathering support to take him down once and for all so that Garlemald's people can be protected.