Going back 2 ex-employer who filed immigration petition required re-initiation of GC?

[gkrr]

Hi,

I am on H1b, I have an I-140 approved (in 2012) with my previous employer (xyz) and this year I moved to new employer (abc) , my h1b valid till 2017 and my new employer going to initiate my Green card processing after 1, 2 months now my previous employer (xyz) requesting me to comeback for strong reasons. in case if i go back to my previous employer(xyz) do i need to initiate my Greencard processing again i.e labor filing etc things? or no need to file anything? just simply apply i485 when dates are current?

Please assist me.