Absolutely they have contingency plans and it's unlikely something with these would cause a jet crash, but in a scenario with instrument flight due to weather,

Absolutely they have contingency plans and it's unlikely something with these would cause a jet crash, but in a scenario with instrument flight due to weather, taking out one of two additional positioning systems adds noticeable risk. Low visibility. No GPS. Impaired ATC. How many additional separate systems have to be affected to be a real problem?