PAA:
Saying that an accidental murderer has an obligation to remain in the city that overrides pikuach nefesh seems ludicrous.
I think the Rambam must be interpreted as meaning that there are no circumstances under which the goel hadam may not kill the accidental murderer should he find him outside the city, not that the murderer is obligated to remain in the city no matter the circumstance.
As for defending your earlier self, I offer you a quotation: