However, it seems that maybe the essence of the original question was not just about the proper status of the position (of course, between two intermediate players that understand the Japanese rules, they would simply accept the position as dead for White without any further play), but rather how to handle the potential practical issues of handling a disagreement that might arise in practice between two beginners??
That is, what should an arbiter do when called over to judge a game with such a disagreement? Should Black be required to state the correct hypothetical line of play (i.e., filling A2 instead of C2 next)? In practice, if I were called to judge such a game, paused during the scoring phase with this dispute unsettled, and if White was trying to argue that it was a seki (and maybe saying something about having ko threats), and if Black simply said something like “no it’s dead as a bent-four and I don’t have to actually play it out because we’re using Japanese rules”, then I probably would feel that Black understands how to hypothetically kill without needing to ask them about any further specifics.
But, what if Black simply said something like, “White is dead here”, and White said “No, it’s seki”? Should the arbiter ask a follow-up question to Black, something like “please provide the hypothetical line that kills White”? If Black responds correctly, then it’s just like above, but what if Black gives the wrong explanation and says, “well, under hypothetical play, Black would continue at C2…” and then White follows up by pointing out that it becomes a living bent-four (not in the corner) in that case? Both players have misunderstood how to correctly determine the life and death status. So, should the arbiter rule it as a seki? Or as White lives? Or should the arbiter correct the misunderstanding of the players and explain how White is dead under the optimal hypothetical play? I actually tend to lean toward the latter possibility, since I think that when the arbiter is called in, it’s their job to help determine the correct status, regardless of some potential misunderstanding by the players, and this is such an elementary position that many should be familiar with. It just seems to be a bit awkward for the arbiter to allow the players make the incorrect determination of life and death, when called in to settle a dispute. Regardless of any potential ways to judge the final position, I think that it would definitely be inappropriate to suggest that the players instead resume the game, and settle things by actually playing things out (since that applies the normal ko rules, rather than the special ko rules used during the life and death determination phase).
It’s also quite messy when two beginners have to figure out how to properly score this situation without any help from an arbiter. They might just both simply misunderstand how to properly apply the Japanese rules. Or, perhaps, it could frustratingly be the case that one of the players is aware of the correct status and the other might not accept the explanation of how to properly apply the Japanese rules. Unfortunately, since the Japanese rules are very complex, and quite unfriendly for fully teaching to beginners, virtually all beginners are just taught an incomplete, oversimplified, and often inaccurate explanation of how to properly determine life and death under the Japanese rules. I think the bent four in the corner is a probably one of the most likely cases where such gaps in understanding are finally brought to light.