Each chain-split where the new chain gain some support always lead to price decline to the current chain, so i would say bitcoin price will be decline a bit for few weeks after SegWit2x hard fork and chain-split.
But this was already proved wrong from bitcoin cash and bitcoin gold fork we have this year.
Both of the splitted chain fails to gain support from both miners and users so it hadn't affected bitcoin's price. However it is also true that if bitcoin2x will get majority of miner's support than bitcoin price can decline significantly.