Travel to US with a valid H1B VISA stamped on passport + approved extension valid from a future date

[CNBN]

My current H1B visa stamped on passport is valid until January  2019, and I have an approved extension I-797c which is valid until January  2022. Both for same employer and no changes. 
1)Can we travel to India-( home country ) and come back in November 2018 with the above two ?its a family emergency so we cant avoid travelling 
2) Will there be any problem at POE?
3) Will the CBP officer give i-94 until Jan 2022 per the i-94 attached to the extension approval?   I am worried because the  i-797 is effective only from future date of Jan 2019
4) If the POE officer gives i-94 validity only until the visa expiry date - Jan 2019 , does our extension get invalid ? Do we have to file a new extension starting from LCA ?
5) Can we get the new extension stamped before the expiry of current one ? If they cancel the current one,while issuing the new stamp, we wont be able to enter US in next 3 months. 

Please advise 

Thank you