I would not be happy about that. One reason I support them is that I see it as healthy for both Cyrodiil and Skyrim to get out of the empire building business. Of course it will depend on Cyrodiil (or Morrowind or whoever) not threatening their sovereignty or borders. In some cases I think you have a right to seize border lands as a buffer zone- though that excuse is used far too often and too broadly. Or in the case of Cyrodiil seeming to be about to fall into Thalmor hands, that might require an invasion. I hope it would be a temporary one.
Weelll... in their waning days, the western empire was forced to make pretty one-sided, ruinous treaties, for instance with the Persians, because they could not afford to split their forces and were continually having to run back and forth to put out fires on the northern or eastern borders and back again. It's actually a pretty realistic setup. Obviously the mythic element comes into play for ES.