The J20 is not for sale, and the J31 is in an even earlier stage of development than the PAKFA, with no concrete support from the Chinese military to date.
Russia is the best alternative at present, but I think this was more of a way to put pressure on the US rather than a serious attempt to get the PAKFA.
Sure. Hypothetically, if the US were to deny Turkey access to the F-35, it would be a number of years before an alternative could even begin to be delivered -- probably 2025 at the earliest, and that's if the direction to be pursued is clear and negotiations go smoothly. That J-31 is a developmental aircraft might even make it more attractive to Turkey by offering Turkish industry more opportunities (and more competitive opportunities) to participate and Turkish AF to have some level of input.
Combat aircraft aside, in the long run I think China should be able to cultivate some level of defence-industrial relationship with Turkey. The folly of relying exclusively on a single nation (i.e. USA) is clear, and a US-European duo isn't much better. Turkey's relations with Russia are currently good, but we do not have to go back far to find when they were not, and indeed the two nations have many overlapping areas of interest where their relationship could become strained. In contrast, China has very little to do with Turkey or its neighbourhood. There is thus little prospect of a Chinese-Turkish relationship becoming seriously strained in the way that could occur with US-Turkish, European-Turkish or Russo-Turkish relations. As such I think China would be a valuable partner for Turkish defence industries.
I suspect there might be some cultural issues to be overcome, as with nations like Argentina that see themselves as basically 'western' and therefore averse to products that are not (even when those products are clearly the most suitable offerings on the market). More specifically, China has arguably yet to prove its credentials at the highest levels of technology and development that are beyond Turkish industry. Most of the products that China sells abroad are products that Turkey could produce itself, even if funds limit what they actually do in practice. But China's prestige in the eyes of nations like Turkey will increase over time. A friendly port call from a Type 055 would no doubt impress.