I am not an expert, here is what I know or thought

firstly, best case is you will still get GC approval with no impact from the laidoff, according to some past cases I heard, that is not impossible

worst case is you can't find a new job, and INS ask you to interview or RFE, you can't provide employment letter, and they deny your GC, then you become illegal and have to leave..

There are many ways to avoid the worst case, until you are asked by INS for employment letter, you are safe to stay here, if you are asked, you can ask your current employer to provide that letter even if they laid you off, sometimes they will do that; or by that time, you might very possibly already found a new job.....since there are so many ways, I think the chance that worst case actually happen is not big

先說the worst case，之後不能找到新的相關的工作：
1．我是否在Layoff之後，還可以合法地呆在美國呢？
可以

在這種情況下，我想H-1B就會失效了，對吧？
對
2．如果可以呆，我將以何種身份合法居留呢？
AOS
可以呆多久呢？
unitl your 485 is denied
我可以自己Renew AP和EAD嗎？
I think so
會影響綠卡的批準嗎，或者說有什麽Risk或Catch？
possible


再說一下the better case，找到新的相關的工作，但在Layoff的時間和新工作開始的時間之間有一個Gap：
1．中間的Gap可以有多大呢？在Gap期間我們必須離開美國嗎？
hopefully nobody cares about this gap, or you can ask for a no-pay vacation to stay employed until you find a new job
2．我可以把H-1B轉到新公司去嗎？
可以, as long as new employer willing to sponsor h1b transfer
如果不行，用EAD可以到新公司工作嗎？
可以
這樣做有沒有什麽Risk或Catch？
if 485 denied, EAD will become invaild


3．AP和EAD可以繼續Renew直到取得GC？
I think so

最後是the best case，在Layoff之前找到新的工作：
1．我必須把H-1B轉到新公司嗎，或者說我必須保留H-1B狀態嗎？或者用EAD工作？
no, you can use your EAD
2．繼續用H-1B(transfer)和用EAD，對GC的申請和批準，有什麽不同呢？推薦用哪一種呢？
H1B transfer is considered safer if you can get new employer to do that for you

again, I might not be correct, just FYI