MSE only supports data backup from Cisco PRIME/NCS.
If mse is down and after troubleshooting there is no way to get it back then you lost the data, no way around it.
Also this is not Cisco official process but I have seen clients recovering from...
Please review the link above (Selecting the Network) and test the following commands, those should be supported:
hi Gavin, I'm afraid there's no way around it .. you have to reset to default.
here's a nice "how to" configure AP's from the scratch ( autonomous)