Do we have to submit another form to extend our stay or, ensure our case is not treated as abandoned if we have to leave?

Our son is a US citizen. Whilst we were in our home country he submitted i-130s, which were approved a month after we arrived here in the US on holiday. As we are currently in the US on B1/2 visas we have just submitted our i-485s for adjustment of status. Our 6 month stay will be completed before we expect an answer on our i-485 application (current 5 month processing time is more than two months beyond the date we have to leave written in our passports).