My EB1A I-140 was denied last week (employer-sponsored). Currently, I am on H1B valid for 2 more years. I want to file NIW and possibly a fresh EB1A petition .But now, the Priority Date in EB2 for my home country is not current for filing a new I-485 (the Priority Date in EB1 is current). 

My previous I-485 was filed concurrently with EB1A I-140, but my I-140 was denied. If U file I-140 in NIW category, can I tie this NIW based I-140 petition to my previously filed I-485 application? and what happens if I leave my current employer? 

Most likely, your concurrently filed I-485 application associated with the denied EB1-Extraordinary Ability petition will also be denied. Normally, USCIS will not allow you to tie the newly filed NIW petition to the previously files I-485 application, because the priority date is not current in the EB2 NIW category.

You can refile an EB1-Extraordinary Ability petition without employer's sponsorship this time, and concurrently file a new I-485 application, the Priority Date in EB1 is current. This will put you back on the pending of status adjustment. Because this new filing is not the employer-sponsored and in EB1 category, you can then change job to work for another employer using H-1B or EAD, while the new EB1A is pending.