Plain answer: No.
You may set the Psoc5 into deep sleep and wake it up every second. Then maintain the RTC and go to sleep again.
Sorry, I didn't understand your answer for my question. Can I not power off the mcu and just run RTC via an external coin battery?
Short answer: No
Reason: The RTC is pure software, so MCU is needed.
This RTC is a real pain!
The fact you should keep the MCU alive, even in sleep mode, in order to wake it up every second does not add ease to the design and the consumption, believe me. I have decided not to repeat this experience, never.
I strongly suggest you to shift to an external RTC fed by its own cell, you add 1 more component to your design, but you go quiet.
My personal thought.