This article is from the FAQ, by with numerous contributions by others.
I need to go back to India urgently for a short visit, however my
lawyer says that I cannot go out of the US, once my H-1 processing has
started. Is this true?
I am not certain why your lawyer said that, but it is NOT TRUE.
While many applications are considered abandoned if you leave the
country during their pendency, that is not true of H-1. The reason:
H-1 is NOT YOUR application/petition. It is your employer's petition.
You can leave U.S. and upon obtaining approval of H-1, go to the U.S.
consulate closest to your residence in India, take your approval notice
and apply for an H-1 visa. Now, INS does not like it. I think there
is a even a regulation that says you must inform iNS about the visit.
In my humble opinion, there is nothing stopping you.