Cats or Lambda Sensors?

[Ronin]

Few months ago I started getting:

16804 - catalyst system bank 1 efficiency below threshold p420
16814 - catalyst system bank 2 efficiency below threshold p430

I've ignored it for a few months thinking its the cats that gonna need replacing but now after driving the car some more and resetting the codes I'm getting:

P0134 oxygen sensor B1 S1 No activity
P1116 - Oxygen sensor heating B1 S1 Open circuit.

Could it have been the sensors slowly failing instead of the cats? I'm obviously thinking of replacing the both lambda sensors now