Hi Tino,
As the S4 chassis needs at least one fabric module for operation, if a chassis is running with only a single fabric module and that fabric fails, all traffic through the system will stop forwarding. For this reason, the use of redundant fabric modules is recommended for these models.
An IO module failure will not affect any other part of the system. Obviously any uplinks would need to be lags spread across multiple blades in order that they are not affected.
Best Regards
Glyn