And likely it would be much worse than that. The Poles were getting better at resisting the Germans and the Germans were tiring, which would mean casualties gained per unit time would be increasing for the Germans.
Indeed, I mentioned that this is a conservative estimate, and exhaustion would certainly be a factor if the Germans want to continue with the same pace - which they have to.
I think the odds are against the generals overthrowing Hitler though. The Germans expected Poland to be a harder fight in OTL, and they expected France to invade deeper into Germany. However, these expectations did not in OTL cause the German commanders to overthrow Hitler as soon as Britain and France declared war. So TTLs war of Poland-versus-Germany with no USSR would lead to something much closer to what was expected. I can't see the generals overthrowing Hitler for that.
True. Not for that. I.e., not for merely having won in Poland but at a noticeable price, and for having lost a bigger morsel of the Saarland, and for not having Soviet friendship and promised supplies. My hypothesis, if you remember it, was that the generals say no - in words, if Hitler will take them, in bullets only otherwise - when ordered to carry out Fall Gelb, the following spring, with a much depleted army due to both these casualties and the need to garrison Poland significantly.
Now that I think of it, the regime will also be under considerable pressure to do something about the Saarland - an idea which a depleted Heer needs like a second you know what, but it's a political issue.
I get what you say about post-war justifications. But another fact to keep in mind is that Hitler would have wanted Fall Gelb in October, and then in November 1940. In OTL. Why didn't such a thing happen? Because the generals said no. And, that time, Hitler grudgingly accepted to wait for the spring.
I tend to believe it will end in a fatal gun-cleaning accident because in OTL, the generals could say: "not now, let's wait for the good weather". In this scenario, they can't set a waiting time of just a few months over winter time; the prudent thing to do would be to wait a full year, in order to rebuild and expand the army. But Hitler will be keenly aware that time is on the enemy's side, that the strategic stockpile of rubber won't last for long, that the Romanians are being difficult with the oil prices, and that the French and British ambassadors in Moscow are offering Stalin the moon and the stars if he'll get down the fence on the right side. So he'll insist.