H1-B extension - I-140 approved -I-94 expiring soon

[tarares]

Hello everyone,
I need some advise here!

My case:
1. I-140 approved with PD Sep 2016
2. H1-B status - (6 years completing) - I-94 expiring on Nov 5, 2017
3. H1-B 7th yr extension filed on Aug 2, 2017
4. Received "Notice Explaining USCIS' Actions Was Mailed" on Oct 12, 2017
5. Extension was filed with an SOW of end date Dec 31, 2017.

I am waiting for my employer to receive the detailed letter from USCIS.

Please answer the following questions.

1. What does "Notice Explaining USCIS' Actions Was Mailed" means - Is it like a RFE? If yes, how much time does one generally get to respond?
2. Can the reason for this status be the end date of SOW.
3. Will this lead to denial of my extension?
4. What happens if no decision is taken till Nov 5 2017 - what will be my options then?

I would appreciate any expert advice.

Thank you in advance.