I see what you're saying. I think eventually people will be getting on lightning and never need to get off. If you have all your sats on the lightning network in a way that you trust and meets your needs, then you'll never really need layer 1. When more people are using lightning they will be able to onboard other people who have never used Bitcoin into lightning as well. There will be lightning channels that persist for years and facilitate billions of transactions. Those lightning channels will have only needed one on chain transaction to be created, so I think 260m is probably enough.