Is stamping mandatory if previous employer revokes the petition

I have a valid stamping with previous employer (Employer A) till Jun 20 2019. I have an approved petition with current employer (Employer B) until Apr 2021. Employer A revoked the petition with whom I had the stamping.
I am planning to travel to India in Feb 2019.
Q1: Is it madatory to go for stamping/dropbox?
Q2: If not will there be any problem at the port of entry?
Q3: My spouse doesn’t have approved i539 (for H4 transfer/extension from Employer B). If stamping is required for us, Shall we go for H4 dropbox/stamping with just my approved petition or is it mandatory to have i539 approved document?

Once your Employer A revoked his petition, all of the corresponding approvals(including the stamped VISA on your passport) would be void. You must get the new stamping done before entering into US.

Q1: Is it madatory to go for stamping/dropbox?
Yes
Q2: If not will there be any problem at the port of entry?
Yes
Q3: My spouse doesn’t have approved i539 (for H4 transfer/extension from Employer B). If stamping is required for us, Shall we go for H4 dropbox/stamping with just my approved petition or is it mandatory to have i539 approved document?
Read my above comment.

Best is to apply for both of you and your spouse’s stamping together using the new approval.

Thanks for your reply.

I just have one more question.
My spouse doesn’t have approved i539 (for H4 transfer/extension from Employer B). Shall we go for H4 dropbox/stamping with just my current approved petition or is it mandatory to have H4-i539 approved document?

Yes, just your current valid H1 is good for her H4