from AP to H1b

A Postdoc, has a schedule to go to China in this May and come back in June by using AP -my boss will extend my contract from August this year,
1) Will my status go back automatically to H1b after H1b extension?
2) Or i need issue this H1b extension visa from other country -like China or Mexico?
3) Or i can not get H1b extension - has to use EAD work.
Thanks for ur reply!