Imo, from a realistic standpoint I don't thing solders coming straight out of POW camps would be in good enough heath to begin fighting anytime soon. I don't know exactly what the major belligerents of WWII actually did with relived POWs, but I'm guessing in most cases, especially if that nation was currently "winning", they were sent back home for a while, if not for the rest of the war. Even if it might not be 100% realistic, I think its fine to just write off captured units as permanently disabled for the sake of keeping things simple and non-politically charged. For a game that abstracts so many other, much more important realistic factors, I don't think it would be keeping in this games theme and scope to go and try to model realistic POW mechanics.
From a gameplay perspective, I'm personally fine with surrounded troops just vanishing and accepting that they had surrendered. I'm also fine with captured units and otherwise destroyed or permanently disabled units being rolled into one all inclusive "permanent losses" statistic. No need for the details imo, especially if they lead to legal issues in some European countries, but it would be nice to have that general units lost or manpower lost statistic.
Also, like others have said, please leave the political stuff out of these discussions. It's not needed to answer the OPs question and will only get this thread locked in the end.
(I'm sure the above comments have been repeated on this forum 10^18 times, but I'm bored and feel like typing stuff right now

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