SRAM X7 front derailleur

[JJDT]

While trying to adjust the front derailleur on my sons'mtb suddenly it broke in half. On closer inspection saw that it completely rusted through the metal.

The bike is about a year old, surely this component should last much longer than a year. Whenever the bike was ridden through mud and every 2nd weekend the bike is being cleaned.

I bought the bike 2nd hand and my question now is can I persue the matter further?

 

Question 2. We are doing the USN event this Saturday and what temporary measure can I implement in the interim untill I can find a replacement derailleur. He always wanted to go 1/10, do I need a new cranset for this setup or how can I utilise the current setup without using the smaller chainring.