Can I cross back to mexico with my temporary visa?

What kind of visa do you have?

Should I been concerned if I haven't received a confirmation letter in the mail?

You haven't received it because DHS doesn't send one.

How to get proof of my admission to the US when I lost my passport and I-94

Get a copy of your I-94 by filing a form i-102 with USCIS.

How to change immigration lawyer while the i485 is pending?

Very simply: contact and retain a local attorney who will obtain a copy of your file either from you or from your attorney.

My son in the UK has a greencard application pending, sponsered by me, a US citizen. He wants to come to the US and work now?

Ideally, yes, so he can enter on a work visa.

Why don't you just buy a plane ticket and leave?

Call to know when will oath taking be?

I don't suggest you harassing DHS during at least the first 30 days. If it takes longer, you can schedule an infopass appointment.

Is it better to take lawyer to the second AOS interview through marriage?

If you can afford one, you should. Especially if it's a second interview since DHS generally schedules those if they suspect fraud in the marriage....

I have had for 12 years withholding of removal status. Can i somehow applied for voluntary departure?

Voluntary departure is granted on court and amounts to a self-deportation. You're probably asking about advanced parole, which is permission to...

Why would green card renewal approval be reconsidered?

At this point, we can only speculate. When you get the decision, takeit to an attorney for an opinion. And yes, it is very possible to lose...