Actually, re-downloading isn't a problem if you make a backup or two. IMO the main risk with downloadable distribution (in terms of companies going out of business) is if there is online activation required to install or play the game. This could be fixed by having a patch created (and maintained if there are additional game patches) to remove the copy protection and held in case any authentication servers are shut down (for whatever reason) or some time limit passes and the game becomes old enough that there isn't enough revenue to justify needing copy protection.
