- They have twice as much money (yay!)
- They have twice as much money but the value is split, so it's worth approximately the same.
- One of the branches wins or mostly wins.
- The split does so much damage that some (all?) value of coins is lost.
Also, by "users", I don't mean holders. I mean entities that actually transact bitcoin on a daily basis. Exchanges and merchants. They can't afford to lose any time (money) on waiting for their favorite chain to win. They have to use the longest chain (and they are the only ones that matter).
Seeing that there is no way in hell the initial split will be anything worse than 75-25 (against Core), I predict that the price will quickly stabilize on the markets after the initial panic (which is already underway, IMHO).
The value of "bitcoin" (the winning side) after the split (and recovery from panic) will have lost an amount equivalent to what "minority coin" is worth at the time (if anything).
This assumes enough hashpower where people can still transact on the legacy chain, and with some sort of replay protection to where exchanges can safely actually convert the funds to have two separate tradable tokens. Right now that doesn't exist, so exchanges won't touch it. This is a huge reason why Bitcoin Unlimited was a non-starter.
I hold some BTC and ETH, is it a case that what I have is no longer holding the value I believed it has?
Right now, the risk isn't that high as the worst case (added uncertainty breaks bitcoin completely) is very unlikely. Instead, (a) one side wins you still have the same amount of coins or (b) both sides win and you probably have +2x the value long term.