Last year H1b.. what are my options for a new offer

I am very less knowledgable about the gc process, 7th year H1b extension etc

My H1b expires in Oct 2013. I have got an offer from an employer who is ready to file GC immediately after joining. However, since my PERM will not be applied before my H1b expiry, I face the possibility of losing my H1b 6 yrs in case there is a query or obstruction
Please let me know if there is such a scenario, I can move from H1 to L2 and once 365 days are over from the filing, I can change my status back to H1b and resume my 7th year extention.
Is that all legal and possible? (assuming my spouse has her L1 visa and remains in status during this period)