I am not an attorney but based on readings, u should be good.. The only hitch could be when (if) u go for Naturalization - they may consider ur leaving the firm as "fraudulent" GC as u did not spend the advised 6 months with the sponsor after GC..
Make sure your severance letter clearly states that the u were "laid off" and did not leave at ur will.. Then, u can state that ur "intent" did not change for working at the GC sponsor forever but u were laid off.. As GC is based on intent, u should be fine..
just my 2 cents..
-ab