Well, that kinda sucks to be honest. On that case, I will be sure to keep my long term storage coins in the original bitcoin format, and use segwit for transacting, but not storing the coins (and I will still use the classic format for transacting if the fees aren't too high)
In the event of a hard fork, anything can happen, including allowing for anyone to steal coins in non-segwit addresses. A hard fork can change any consensus rule; there are no restrictions, so even having your coins in non-segwit addresses would not be safe. This is only a problem if you expect that a hard fork should happen that everyone agrees to that would allow anyone to steal segwit outputs. That would mean that there would only be one blockchain. However IMO any such hard fork would be contentious (after all it would allow for stealing funds) and there would most certainly be two blockchains - the original which still has segwit activated, and the one that does not have segwit activated and thus coin theft.
In the case a hardfork, what would happen to your BTC if the BTC are held in a lightning network hub/channel thing? You would also lose them so you need to move them back to a legacy format address?
Since LN uses segwit, yes, such a hard fork could result in stolen funds there too.
I don't understand why you are so concerned about such a theoretical hard fork. It would be a hard fork to deactivate segwit, which means that it would be contentious and lead to a chain split like Bitcoin Cash did. All that would happen is that a new altcoin is created. The thing is, with hard forks, anyone can make a hard fork at any time that changes any consensus rule, including allowing for the theft of coins. For example, I could make a hard fork right now which simply allows me to steal all of your funds right now. But that fork would be an altcoin, and no one would pay attention to it. I think you are giving too much credit to such a hard fork even existing, let along being a threat to anything. If such a fork happened, it would almost certainly be ignored by the majority of users and just become another worthless altcoin.
You are right that a hardfork that doesn't include segwit would get ignored by the majority of the community and would therefore become irrelevant, but Bitcoin Cash was also supposed to become irrelevant. I mean don't get me wrong, it's pretty irrelevant, but if you managed to dump at the top, that was a lot of "free BTC", and it looks like all you need to get a hardfork and some hashrate is a couple rich people with the right tools (propaganda, buying hashrate and then pumping the price on the markets) to get a hardfork going.
Even if eventually it becomes and irrelevant altcoin, there's a period of time that if you make hte right moves you can profit from the clusterfuck and get yourself free BTC from the fools that are buying the hardfork.
If someone with the enough resources decides to hardfork BTC into another fork that has no segwit and has 16 MB of blocksize, you want to be able to get your share of coins and dump it, and if you are holding everything on segwit you are going to need to move all of your wealth into the original format, which once again it's a problem since you can't send all of your BTC in a single transaction if you want to retain privacy, same goes for when you want to dump your coins, so you would need to go through a real annoying process of separating transactions.
