That's a complicated question and answer with a lot of variables. Are we talking about gam-gam with multi-organ failure on a mechanical ventilator who has had chronic pain for years and just prayed to Jesus to send her home? Or are we talking about a 20 something athlete who just collapsed on the field of play and received immediate attention? Because both of those get different answers.

It's difficult to say if the person is recoverable, but as long as you continue chest compressions without major interruptions, some blood will continue to circulate and should mostly stave off irreversible brain damage. Even without rescue breaths, there's a massive benefit https://hsi.com/blog/are-rescue-breaths-necessary-during-cpr

A medical doctor friend some 30 years back said patients coming back to consciousness after reaching the hospital after 45 minutes of CPR definitely did happen.

He also said that if you enter the hospital on a stretcher, you're most likely also leaving on a stretcher...

The chance of 45+ minutes of CPR allowing someone to recover to even near normal health is tiny. The right question to ask is, do you care enough to cling onto that tiny hope? As in, is it your child or loved one? (Or, is it your job to administer CPR while the patient is being transported to a hospital...)