OpenDiablo2 VS IMCUnlockLite

Diablo II: Not currently, though possibly in the far future through projects like OpenDiablo2.

There is a an open implementation that you might be able to use: https://github.com/AbyssEngine/OpenDiablo2

If its not setup already, yes you just install, run and choose unlock. Its recommended to disable your plugins before you do.

Else, the card is necessary for a 1000 model. My advice is to buy a used 4GB ($10-$15), setup the hack, then install imcunlock lite. This will give you access to a 1GB internal storage, similar to a 2000 model. This partition is available even if the hack is removed, so it completely removes the console's dependence on memory cards. Then sell the 4GB memory card back into the market for what you paid.

If you have an OLED, use imcunlock lite to create a internal 1GB storage (removes dependency on memory card, even when running stock).

Definitely sounds like memory card failure. Only option is to buy another memory card to run homebrew applications. Next time you might want to look into imc unlock lite; this application will create a ~1GB internal storage on your OLED (similar to a Slim). This way, if your memory card ever fails you can revert to imc0 partition as a backup.

If the Vita is a slim, you don't need an official memory card as it has a built it memory. If its a phat oled consider this. IMCUnlockLite / IMCUnlock (if your not sure what your doing stick with the lite version). This is an option, use it as your own risk.

Once you have sd2vita setup, look into IMUnlock Lite to create a small internal partition, similar to the internal partition on a Slim. This will protect you from requiring a memory card once sd2vita is setup. In fact, I know people that have bought a used 4GB from Gamestop, setup sd2vita then IMCUnlock, and returned the memory card to Gamestop.