Your question is a great one, however it only applies if you own your wallets (which most people do). It would not apply to wallets held with Bitcoin banks, like Coinbase, Xapo, Circlee, or Freebitco.in.
What ever you do, don't follow this guy's advice...
You could do what I did. Sell every coin you have and wait until the community gets their heads out of their asses then buy them back later, maybe.
The community has been debating whether and how to fork for over a year now. If you'd been out of the Bitcoin market for that long you'd miss all the appreciation of price we've seen over the last year.
A smarter move, if you're really worried about the coins setup post fork, is to convert your coins to a Coinbase, Xapo, or Circle account. They'll take of all of this for you.
If uo keep them on your wallet, and the chain splits, x coins would result in x coins in one chain and x coins in the other.
If you keep them at a "bitcoin bank", the bank may refuse to give you the coins on one of the chains, something like this happened when ethereum split (some "wallets" refused to give users their ETC).
Keep them on a paper wallet, and then, if you think it is wise, trade them after the dust settles.
I see your point. Why not have a few coins in each chain. I sold what I had left above $1,200 (230 btc). I got a little under $300k for them. If the btc/usd exchange rate drops back below $1k per coin I will buy back in for $50k just to hold for the chain split. Then even if I lose everything, which is highly unlikely, I will only have lost my profit.