Why would Ghetsis not leave Unova at the end of B/W? He knows he's a wanted man, so of course he's going to leave the region. He's not stupid enough to stay in Unova after his true plans have been exposed and thwarted (for the moment, anyways). Why else would Looker be searching for N first? He obviously doesn't have any other leads on Ghetsis, and if Ghetsis were in Unova, then I'm pretty sure it wouldn't be hard to find him.
Also, I don't think the Shadow Triad were telling the truth about not knowing where Ghetsis is. They had no reason to be honest with the player character in the post-game. It's literally their job to be deceptive and mislead anyone wondering where Ghetsis is.
And finally, I don't think Akuroma cares about the police apprehending him. I think he's being deceptive only to mislead the player character. Let's be honest, the presence of any sort of "police" in these games has been almost non-existent, and every villain knows this. That's why it's always up to the player character to stop them.