RFC lookup in case of backend maintenance SAP PO

[ramu_g4]

Hi Experts,

We are working on synchronous interface with RFC lookup(calling Function module on SAP Backend) like shown in below picture. Based on the RFC lookup output value received from SAP S4, the incoming request has to be either forwarded to system B or system C & get back the response.

This should be ideal scenario when SAP S4 is up and running like shown below. There is a mapping defined with RFC lookup in this case and this scenario works perfectly fine.

But, now in case of when SAP S4 is down during maintenance mode, the incoming request should be always forwarded to System B. In that case, we have also defined different mapping to be executed without RFC lookup & The corresponding response received from System B should be send back to System A.

Is it possible to execute one mappings when system is up and another mapping during maintenance window.

How SAP PO system will get to know when there is SAP S4 in maintenance mode?

Thanks

Ramu