The reason why Prussia is 'alive' in Hetalia is following...
Hetalia plays in WW2 and some other certain events before 1947.
Prussia was dissolved in 1947.
That's why we see him there. Prussia is still a country there.
You see... The Berlin Wall wasn't far away so Prussia directly personified something.
Hetalia does not play in the 21st century.
If Himaruya would make a new season, Prussia probably won't appear.
There is no reason that he is alive.
It's just the place in time.
Prussia is dead nowadays.
And there is nothing to disagree.
Prussia is dissolved, Germany united and I doubt he is a Micronation.
So, yes. He is dead.
It's just a big mistake because of the place in time.
さようなら
-日本