Shenzhou would certainly have flown more or less as is. Assuming participation doesn't increase funding I'd think they would probably only fly about once a year and it would be more along the lines of supplementary Chinese crew members being aboard for a few weeks at a time (longer than the old Russian visitors and current tourists who come up for a crew rotation, but quite a bit less than a full tour). Given the requirements placed on vessels before they dock I'd think that by today's date we'd probably only have had one or two Chinese missions so far, with nothing happening until some sort of docking away from the station had been demonstrated. If I had to guess there would be a Chinese module in the works, but it would be a few years out still, taking the scientific bits of the currently planned station and negating the need for independent flight capability.
All that said, frankly I question whether it would make sense for China. I would quite like to see them participating, but all things considered an independent program seems better suited to their goals. That said, I don't particularly understand their intent to build a full station either, enhanced Tiangong like labs seem more suitable. Basically Chinese VISITS, starting now that they have shown an independent capability, possibly even docking a Tiangong to the station on a semi permanent basis make sense to me, but not full partnership. Ultimately the Chinese program is for the most part about technology development, military applications and showing the flag, all of which are better and more cheaply served by an independent program.
If I had to guess the actual trajectory things will take is that now China is openly committed to an independent full station that will happen for propaganda purposes if no other. It WILL probably be significantly delayed between cost and the ability of Tiangong 2 and 3 being able to accomplish all real mission objectives of a station, and the final project may eventually amount to little more than docking a few Tiangong's to each other. In any case, once something they can call a station is operation we'll see a Chinese visit to ISS organized once it can be a bilateral program that includes an international visit to the Chinese platform (be it Soyuz or something American).