Point about escaping/pardon. I acknowledge that society is ever so slightly safer when exceptionally dangerous criminals are executed.
About the risk of being pardoned by a malicious state, it's true... But the other way could also be true that a malicious state can execute people who don't deserve to be executed, like Snowden... Perhaps a compromise is to make particularly heinous crimes unpardonable? That would be a decent alternative to the death penalty, and it would be very difficult to repeal such a law.
As for escaping prison, it's already rare that someone escapes from it. The solution is making better high security prisons for the most violent and dangerous criminals. I think it's definitely possible to make escaping so difficult and dangerous that it wouldn't be a problem. Make a prison on an island or an old oil rig, implants to track the prisoner's location (a fancier version of the anti-theft tags in clothing stores), random X-rays to check they don't have anything hidden in their bodies. All of these are definitely better than executing someone, though personally I think that maximum security prison breaks are already so rare it wouldn't be worth it.