I have heard and read this discourse for sometime now and this has been opinionated by the Pakistanis themselves, of course by the liberal lot, people who are invariably members of SAFMA.
Are the sino-pak relations really strained? Yes, but I strongly believe the pros of having Pakistan alongside will most definitely weigh on the cons, and so the two will cling on irrespective of the circumstances.
# Chinese understand fully well, a vacuum in Pakistan means open doors for the US and then these two countries together could cause a lot more pain to them. China's encirclement will be happen on another front.
# Strategically China uses Pakistan as a buffer zone, as a point of transit in case of choking of Strait of Malacca, and most definitely in containing India, a regional rival of today and possible global rival of tomorrow.
# There is the added factor of terror.
# There remains the question of access to Indian Ocean, the trade route, the silk route.
# Most important, if China is to rise up to challenge the US for the top slot, they will require as many proxies as possible, and Pakistani leadership is game for it and is a perfect playground for the same.
China and Pakistan drifting apart, no, not happening.