Job change based on old approved I-140.

[tablefan]

Hello experts,

My H1B status kicked on Oct 1, 2009.

Employer A filed I-140 and approved with priority date Nov, 2012. I left this employer and employer did NOT revoke this approved I-140.

Employer B filed H1-B- Full Time in 2015. This employer also filed I-140 in 2016. This I-140 case status is pending. Attorney is expecting to get result by end of June 2017. H1-B has been stamped on passport with validity Nov, 2018. I-94 validity matches with H1-B validity. 

Employer C filed H1-B- Part time (concurrently) with validity April 2019. 

Questions for experts:-

1. If I leave employer B tomorrow, can I be still under valid H1-B status? Can concurrent part-time employment helps in maintaining status?

2. Do I really need employer B's approved I-140 before transferring H1-B? Can employer A's approved I-140 be sufficed?

The best case scenario that I am thinking is to leave employer B after 181 days has elapsed from the date of I-140 approval. 

Thanks!