How difficult it is to get a TT in the U.S. after leaving the country?
Q1. Is it possible to get a TT position in the US after leaving?
Yes, it is possible; I have done something similar (in Computer Science). I left the US to do an extended PostDoc and then returned to the US as a professor. This worked out for me in particular because I had experience and expertise in a specific area that the school was looking for. (And &gt;40 publications by the time I returned.)
Q2. Will my work experience outside the US be counted/valued?
If you are productive there typically is no reason it won't. In particular, you need to continue to publish high quality work at top venues. This may be harder to do if you don't have good students. In this case you may look for good collaborators and do things like invite their students for research visits.