Jumpy - I THINK from what I have seen that GPWS WAS working (gear warning?) so I guess the radalt had not 'failed' but simply misread?
With the #1 RADALT INOP only modes 1-4 are inhibited. Gear warning is a function of configuration and altitude so it would still warn the crew. What will not function is the warning below 1000 feet to 500 feet "too low gear".