Pack--Not sure I see the scratch in bottom pic as described. While the G10 can focus 1cm from lens in wideangle (28mm equivalent end) it focuses well beyond that (300mm?) when zoomed out. I wouldn't think you would use wa to shoot macro, due to flash problems this close, consequently the scratch wouldn't be in focus. (Just like dust etc. on a lens filter isn't in focus.) Serious backlighting could cause some diffraction I suppose but not likely underwater. If you aren't shooting macro it would be even less likely to show.
To counter all this, you get to see the scratched surface whenever you grab the case to use. Painful reminder. Even if some clown

far away tells you "Why worry?" if you really could get it dealt w/ or reduced by a
glassier (say what?) for 15 whatever kinda bucks, why not? Buying a replacement glass (which now seems unlikely) and hoping that after removing & reinstalling there are no leakgage problems, well--I dunno. I think personally that would be on my mind more than the scratch.
Question: if you shoot a white wall or bright sky etc. in macro (on manual focus) do you see it? That might help with your decision. Continued good luck on this! // ww
ps--When I signed up on SB I meant to use wonk and never paid attention to it--until someone on Phillipine Divers pointed it out later. I guess if the mods or someone wants to toss me out over it, well--what the ****, eh?