Sorry to hear about this!
At release Last Epoch will support both online-only, server-side characters and offline-only, locally stored characters. The former are coming during Phase 3 of our Early Access Forecast.
This thread was added on April 02, 2020, with posts from Sarno.
Next week we’ll be discussing ways of improving the reliability of saves.
What I’d say at the moment is that ensuring that the game client is able to close down normally helps, as otherwise it can cease running while actively writing to save data, which is bad.