I can absolutely understand why Warped Tour would be ending. I think the reality is that the music Kevin is showcasing within Warped Tour just isn't getting the attention that it used to receive, which leads to lesser crowd turnouts. Plus, there are just so many artists that are repeats at the top of the festival almost every single year. On a personal level, I had a really good time at my one and only Warped Tour in 2016, where in 6-7 hours of time I saw not one single song I had ever seen live prior to that day, including just walking by sets as I went from one area to the next. It was so much fun to see Yellowcard, NFG, Good Charlotte, Atreyu, Sum 41, etc. for the first time. Overall, I think I mostly worry about the future of the music that I am passionate about. Warped Tour was very much the biggest outlet for a lot of those artists to establish themselves on, and it was the only guaranteed festival that most likely landed near you on a yearly basis showcasing a lot of these artists. There are casual fans who literally attend Warped Tour as their one show every year, and I think that does hurt the potential exposure for these artists.
You have to buy a ticket for each different show. I am unfamiliar with the different tickets this year. Every year I have went there have been tickets available at the door the day of. Every so often there are bands that will surprise certain days but it is a small chance. Some bands do not play every date so make sure to check the bands you want to see to see if they are playing the date you are thinking it going to. What bands play which date is on the Warped website. Have fun!