At the end of the Li River cruise, how do we get back to Guilin? who do we boon the river cruise with

After the cruise, you can make a visit to West Street in Yangshuo or other places in Yangshuo and then go to local bus station to take bus going back.
For the second question, I am afriad that I cannot grasp the meaning of this question, so would you mind give me more information about it?

Who do we book the Li River Cruse with?

Hi, I recommend you book that through TravelChinaGuide, which is trustworthy. Just send them an email at travelchinaguide.com|booking by writing down your requirements and they will book that for you. May help!