One of BTC's big selling points is the network effect, and if you split you obviously will have, at least initially, a decreased network. How bad will probably depend on how split they are. If it's one chain at 95% of pre-fork hash rate and the other at 5% then I think the price damage will be a lot less then it will be as we'd approach a 50/50 split. In fact, based on tons[1] of incontrovertible[2] evidence[3], I will create that metric. After a split, total price (BTC+BTU) will equal that of the pre-fork BTC price multiplied by the percentage of the total hash rate that comes from the longest chain.
BTCprice + BTUprice = (Longest chain hashrate)/(Combined hashrate)
So, if it forks near $1000, then after as the hash rate of the two forks approach 50/50 we will approach a 50% price drop, so BTC+BTU = $500. But if say the largest chain has 90% of hashrate, then we will see prices around BTC+BTU = $900.
It is an interesting calculation based on the % of the fork at the time, although it is not mentioned as much difficulty readjustment is an area that will impact the prices for a while until we retarget to the next 2016 block set.
If it is 95 to 5 then the time it will take for the retarget may be quite a while for the second chain and push the price downwards till it readjusts while the chain with more hash will see an increased % of usage and profit and readjust without much issue.
On the other hand if we go by node count reliable relays would need to change to the fork chain from the original and a fair amount of user nodes are lagging so both chains will relay.
Scenario 1 55 to 45 will mean that it will be about a 20 min block so a readjustment won't take as long as 95 to 5 in terms of difficulty retargets.
The % will be divided by how many merchants accept the new version versus the old version as usage metrics matter just as much as miners.
If for Example Canada Bitcoin merchants remain staunchly core and refuse or deny services to BU for the immediate transition period then people will have to stick with one chain until the services appear that support the fork.
If they do both coins right off the bat speculation could have a field day and after the giant dumps of the chain people don't like prices could easily rally back. Assume a 30-50% Discount as both sides strongest proponent supporters will dump the coins of the chain they disagree with maybe only keeping 20% of it vs 80% of the chain they like more. Resulting in a median dump of the price.
Over 12 months assuming people wake up Bitcoin will likely scale back from increased interest and end up positive for the HODL position.
But people love to play with fire and you either get wrecked or make a killing either way both sides would be on sale for a while just cause people rage dump or so we are led to believe ^^.
In simple terms people dump the side they don't like but will also buy more of the one they support but keep a bit in cash hence it reaches an equilibrium, new investors will see two coins think a sale is going on ... buy more ignorant of the split or internal issues. (Mainstream lol)
Ecosystems grow $$$.
