Do you mean for comm loss? If there is local power loss, how does the PLC keep functioning?
I’m sure others have more informed suggestions than I do, but for what its worth…
There are quite a few hardened industrial, fanless PCs available. I’m not sure if you meant reliability of the PC hardware, or the software. FactorySQL of course does what you describe (including local data caching on comm loss), but certainly requires a PC.
I think there are various hardware dataloggers available. Perhaps your requirement for local control limited your search? Maybe a 2-device solution would work best (cheap PLC for limited loal control plus hardware data logger). I’m not sure how these hardware dataloggers work - I don’t know how you suck the data out of them.
Good luck!