You haven't needed a disk to play D2 in over a year, since the base game went free-to-play when Shadowkeep launched. Due to the way PS does things, you would have to delete and re-download the game, as opposed to just not using the disc, so if you want to do that, you may as well keep using the disc until the Beyond Light download becomes available, as that will require a full re-download of the game. Might as well only do that, rather than redownload now, then again in a couple more weeks. For PC, you just need to download the base game through Steam for free, and then set up cross save with PS as your primary account, and you'll then have access to your PS characters on PC as well. You will also have to buy any paid DLC on Steam (Forsaken, Shadowkeep, Beyond Light), or you will not have access to that content, even if you have it on PS.