You don't still have your save files?
I don't like going back to old saves, once I'm done with them. I'd rather experience new content with a clean slate than with all the baggage from a playthrough done years ago.
The game supports cloud saves on both Steam and GOG, so whichever version you used should have the save data backed up online (for GOG I think you need to be using GOG Galaxy for cloud save functionality though). While cloud saves are nice, I always manually back up my saves for every game I play too.
Yep, this game actually had some pretty awful cloud save mechanics thanks to autosaving. Granted, I think you could turn it off but at significant risk given how much could happen in a short span of time leaving important events unsaved, but I left mine on. For most probably not an issue but after close to two dozen playthroughs I maxed out what GOG and Steam save limits were and eventually just made a local backup of the important stuff and would then regularly delete cloud stuff to keep it to a minimum. I've ended up using a similar strategy for Oblivion Remastered but more so because MS really screwed up that one.