I never said that all the people you say were murdered by the Nazis were settle somewhere else. You're creating a false dilemma in which we must accept one extraordinary claim (huge numbers of people were buried within impossibly small spaces) or another extraordinary claim that huge numbers of people were stealthily resettled.
But there's no false dilemma. One can of course think of alternative explanations, such as Nazi UFOs abducted all the deportees, they are simply not very probable, even downright implausible.
It might be that the deportees never reached BST, because they jumped off trains, alive, and either survived or were caught and shot, being buried in a variety of localities and their bodies either found or not found after the war. It wouldn't account for all the victims, but it might affect the totals a bit, say by 1%. There are also reports of trains stopping to offload bodies of those that had suffocated en route, so that some of the deportees died and were buried before they got to the camps. Again, not many, but it's another factor that can be pointed to. More plausible, of course, than Nazi UFOs.
It might also be that the deportees all died en route to their 'real' destinations and are buried, or were cremated, elsewhere. There is not exactly a shortage of mass grave sites in Eastern Europe.
These are just some examples of alternative explanations, none of which add up to survival.
All evidence, however, points to the deportees being cremated at the camp sites, and not being abducted by Nazi UFOs or being buried elsewhere.
We can prove whether or not huge numbers of people were buried at these camps. If they were not buried there, they must have gone somewhere else.
Or, you need to revisit your original premise that there is anybody missing to start with.
The false dilemma is in your 'if... then'. Your 'if... then' is a deduction, not an inference. You have presented no evidence offering any alternative explanation for the fate of the victims. The absence of such evidence ought to prompt you to revisit your original deduction and see whether you aren't in fact grossly mistaken.
Which you obviously are, since your 'if... then' is also premised on a strawman, which has already been disposed of - namely that the bodies of the victims were all buried at the camps and should have been found there.
The sum total of evidence indicates that the victims were cremated, and that these cremations were ongoing for at least some of the victims from a fairly early stage (in the 'Lazarette' set up in all of the AR camps), and from a certain point on (varying between camps) all new victims were immediately cremated without being placed into mass graves. Therefore, not finding
bodies to the tune of the number of presumed victims cannot refute the claim. Nor is determining the size of graves going to produce more than a rough guide to the number of victims, since some of them never were interred. Moreover: the sites were trashed after the Nazis left by graverobbers, resulting in disturbed crime scenes, in some cases quite seriously disturbed. As the ashes and cremains were also partially removed from the site, nor can weighing ashes or counting teeth or any other method help us determine the exact number of victims on-site.
You are of course free to seize on these uncertainties to claim that we cannot be 100% certain that x number died at BST, but this has been entirely self-evident ever since the end of the war. To reduce the most probable death tolls therefore requires external evidence, as for example was found with the Hoefle telegram, which reduced the Belzec death toll from 600,000 to 434,000. The discrepancy, it turns out, consisted of victims shot on the spot in western and eastern Galicia, and can be found for example in part in the area of the former Nazi Distrikt Krakau in no fewer than 78 mass graves containing 60,000 bodies of Jews shot to death by the Nazis without ever getting on a train for anywhere.