not sure how the hound and arya will meet since the hound is already much further north and headed towards eastwatch. arya will go as far as winterfell at most.
the riverlands are likely under martial law by the lannisters seeing as how arya ran into a contingent of lannister troops sent there to “keep the peace”. long term, it’s likely another riverlord deemed most loyal to the crown will be raised up as lord paramount.
at this point the stormlands are likely lightly or undefended, since renly’s army joined stannis after renly’s death, and have been decimated following the blackwater and stannis’ final stand. any deserters or stragglers are likely still stuck in the north and probably won’t make it home for some time, if at all.
ellaria sand and her daughters had taken power over Dorne but with so many of them out of the picture now it’s anyone’s guess. the Martell line is extinct in the show as far as we can tell.