I doubt Popa will resign. I doubt the FA will sack him.
We were always said to not be getting out of the group, and we did, So the FA will see that as a pass. We were not expected to beat Turkiye, and we did, so FA will see that as a pass. They will also look at the young age of the squad and see it as a pass.
However, three key things stick out for me.
1) His unwillingness to adapt his playing style even when the opportunity presented itself. When we had a chance to really press on, he made changes to the squad that ultimately cost us. Some might argue that shows his willingness to change, but it was actually the opposite. He tried to double down by bringing in Leckie - a player he favours - to be more defensive and hopefully counter the US more so. It failed. Not Leckies fault.
2) His bizarre tactics with this penalty shootout. Having 3 defenders listed in your 5 either shows that your attackers need to be doing more work, or that your penalty plan is shit. Also, having Matt Ryan only know with 15 minutes before is shocking. Beach had earned the right. Our best player all tournament and you take him off in such a big moment. Goes to show the inability to adapt to the situation.
3) The negative tactics. Even when in control in games, he didn't push that advantage home. We started strong against Paraguay, and then he just went limp. There's a reason that game was dubbed worst in the tournament. The stats also had us in the bottom 5 of many key things. You can't be expecting to progress with that kind of figures.
Like Barca4Life said, so many resigned after their failed campaign. Some top quality managers. The FA has an opportunity here. We have a young squad with so much potential. Do we want to waste years of their progress and talent on this drab negative crap football, or do we want to be progressive and get someone in who can actually develop these players. I know many say the money is not there, but honestly, I'd be going with an international option. I feel we do have the means and the ability to do so.