Would prevention by law, of slaughtering at Mina be sufficient to realise the inability to carry out…

Answer

Fear of consequential harm for breaking the law should lift the obligation of slaughtering at Mina. It must not be understood, though, that slaughtering elsewhere would make up for slaughtering in it. However, what makes slaughtering elsewhere in order is [indeed] Mina’s small capacity to host all pilgrims as discussed in Manisikul Hajj. Apparently, slaughtering was made impossible, for the reasons mentioned in the question, not for the smallness of Mina? Therefor, combining both slaughtering outside Mina and fasting in lieu of hady (sacrificial offering) should be in order, as a matter of ihtiyat luzumi.