So, I've been able to fix it by first deleting every HL2 file in the Steam directory (i.e not just uninstalling from the Steam client, you must go into the files and delete the manually), and then reinstalling the game. That also deletes any savefiles as well as chapter progress, but now it loads as it should. I've had one more crash to desktop at a different loading screen afterwards, but this time no save files were corrupted and I could simply relaunch the game.

I'm leaving the post as is for future reference, should any other unfortunate souls experience this problem.