H1b renew or extension or amendment

[palh1b]

Hi , i have h1b till july 2018, however am carrying and going back to india this month.I was here for 4 months only. Mostly wont be able to come next year as well.

Question : i will change my job end of 2017, in case i am not able to file out for extension , will the visa expire completely.

what are the options after changing the company in india, to make the visa extended, so i may be able to travel back in 2018 to continue work here  .

do i have to be working with current employer to get a renew/extension/ amendment for my visa?

Thanks in advance!