Sony is not deleting your act.dat. The only people i have seen this happen to have manually deactivated their system/Done a system format/Edited their Registry file changing the PSN Details and an IDPS would not cause your act.dat file to be erased if you where IDPS Banned you would not be able to log into PSN at all with that system. there is no code that exists in 3.60 that will delete your ACT.dat file except doing a system format or going into the system activation menu and selecting deactivate, if there was code that could just delete your act.dat file it would have been found long ago and Sony would have used it long ago. This change was server side its not possible for a firmware that was made 4/6/2016 to magically have code added to to auto erase a file it if you didn't update, the only other way to have a system deactivated would be for you yourself to go to Sony's website and do an online system deactivation of all your playstation devices, If they deactived your system go to the website and see if its shows up as an active system (Which legally they would not be allowed to do). If Sony was to delete the act.dat files of people below 3.65 thus locking them out of legit purchased games just because they didn't want to update they would be open for a lawsuit for disabling peoples systems. They are legally allowed to disable PSN Access but they are not allowed to intentionally brick or disable its ability to play games they where legally purchased
I have a spare vita that was in the enso beta since the beta was released and i have been Logged into PSN with it ever since, it is activated and I have tested all day yesterday and today when rumors of it auto deleting the act.dat file started, to get it to delete my act.dat by going in to PS store and attempting to download games getting the error code mentioned and playing games on PSN it has not once been deleted.