got H1B extension for 3 years in 5th year through i-140 is not approved

[shibag]

My Perm(labor certification applied) is still in processing stage.

My h1b extension(for 1 year) was applied in 5th year but I got 3 years of extension instead of 1 year i.e 6 years H1b limit.

1.can I stay in US through 1-140 is not approved( in h1b 6th year) since I-797 is valid for 3 years ? 

2.If I go INDIA for stamping will I get visa for 3 years or is there  a risk ?

3.If in case stamping is done for  3 years , will immigration officer in port of entry give 3 year of I-94 validity ?  

In case I may not get my i-140 approved within 6th h1b year , is it safe to stay  in US since i-797 is valid or  spend 3 or 4 months working from INDIA to capture some more extra time for i-140 approval.

Thanks in advance