From my neck of the woods, we've largely viewed the Americans as part of a security arrangement (Pacific) but, as a trading partner, they are far behind the Chinese (so much so that its a constant political discussion on how to balance the two competing alliances).
This is largely what Trump was trying, and failing (miserably) to address with his tariffs, nobody buys from the US anymore.
If the fibre was cut through the USA, then yes there would be a period of difficulty, but it would be very quickly replaced with other countries technology (keeping in mind that most Western governments were looking to move to Chinese Huawei telecommunications kit until the US made aspersions as to how secure peoples data/secrets would be if that happened, completely ignoring Snowden's revelations that the US had been engaged in using the hardware in overseas telecommunications systems for that exact purpose)