Let us know what you do and the result. I had a similar issue where Win10 did an update and then got stuck, rebooted and it tried to roll back and I ended up with no Windows. But uncertain as it does not go to the dual boot screen if I need to reload the Telcast firmware. Reading the post on here it seems the issue might have been using the Micro SD card as transfer drive as there was not enough memory to do an update on internal storage. I’ve ordered a 3 OTG powered adapter and will try loading Windows onto the old partition when it arrives, if this does not work I will try the Telcast 16Gb OS files.
To be honest after thinking about it and using the tablet a few hours whilst it was updating I kind of think I would be better off having Win only tablet as the only benefit of Android is some software I already own which I can get for Windows anyway. The extra memory for windows would be more beneficial than Android. I don’t think I can make a A5C8 single boot. Would be nice if it could set the partition sizes differently, 16GB Android / 48Gb Windows would suit me better.