J2 to B2 Change of Status

[SGAU]

My J2 visa expired on 15th October 2017 and I applied for I-539 to change to B-2 status. Decision on I-539 is still pending. My I-94 is stamped with D/S. My spouse, J1 principal applicant, applied for green card on EB-1A. I-140 is approved and we are waiting for her I-485 approval. Once her I-485 is approved then I will proceed for consular processing.

1. If I-539 is not approved or denied in 240 days do I have to leave the country on 240th day? If not then how long I can stay in this country. 
2. If I-539 is approved, can I file for B2 extension for 6 months, I am assuming that by that time I-485 will be approved and I can proceed for consular processing.