回复：so as long as the employer does not withdraw I140, the person

as long as he wants to find another job and transfer to H1B once he gets an offer?
-Yes if he can find a job in short time e.g. one month. Otherwise, he can change his status to another nonimmigration status such as H4, F1, B2, etc. Then he can change it back to H1 again after he find a job later if the approved I-140 is not withdrawn.

Does the guy need to re-apply PERM and I140 on the new job?
-Yes if he want to get the GC because he does not have a pending I-485 when he lost job.

I assume as long as the new job is in the similar field, he can still carry the PD.
-Yes, he can use the old PD for the new I-140.