you are legal.

So, does it mean if i can't find a new job for six months (just an example) after being laid off, I'm still legal?

You are legal as long as your 485 will not be denied or was not denied. Or you have transferred H1B to another company if, unfortuantely you received 485 denial notice.
Say,you got laid off within 6 months, but sponsored company will not revoke your 140. You will be still legal to stay, legal to work in another company using EAD.
Usually when CIS adjudicates your case, they may send an RFE for employment verification letter. Then at that time you should be able to provide one.

What kind of status will it be, I-485 pending?

You are on AOS/H1 status.

Actually I'm under H-1B now. I'm afraid that I can't find another employer right away in order to do H-1B transfer. So, if it happens, I have to stay with the status of I-485 pending and give up H-1B, right?

If you cannot transfer H1B in time, just use EAD to work and get another fulltime job, within 6 months. Then file AC21 when you pass 180 days after 485 filing. This is safe.