Currently, patch 0.9 is planned to be exclusive to Steam and it’s unknown at this time if this will change in the future. The following are some quotes from Mike Weicker, a senior developer/designed at EHG, explaining this:
Nothing will happen to your current characters. They are considered offline characters and are playable in both the stand-alone client or the Steam client of the game. Both clients use the same location to access and save your offline characters, which can be found at this location on your computer:
C:\Users\Your_User_Name\AppData\LocalLow\Eleventh Hour Games\Last Epoch\Saves
No, though you will have to link your LE account to your Steam account so you can access the game on Steam if you wish to play patch 0.9. The following support article explains how to do this:
https://support.lastepoch.com/hc/en-us/articles/1260805145970-Steam-Account-Linking
When patch 0.9 releases, your previous characters (all 0.8.5f and prior characters) will be playable in the “offline mode” of the game. This “offline mode” will be similar to what we currently have on live (meaning it’ll still require an internet connection) but should transition to a more pure offline mode in the future as Judd Cobler, EHG CEO and game director, states below: