A/P ALT re-clearance
I personaly think that the A/P feature that you are referring to might be usefull in cases of decompression at hight altitudes without a descent being initiated by the pilots - assuming that for some reason they did not have enough time to don the mask and went incapacitated (not following the 'above FL410' requirement to wear oxygen mask) - then of course you would need to solve the problem of where the aircraft 'puts down' itself? But other cases - for example like in the case of the Cypriot 737 that continued climbing I think it would be sufficient that another cabin alt horn sound would go off again (while being silenced at FL100) when the cabin alt reached eg FL140. All of the onboard systems assume that the pilots do their job properly (unfortunately not the case of the Cypriot plane)...