It seemed like no one answered your question, but I stopped reading part of the way in lol
Anyways, just posting to answer your question OP.
According to what was said/leaked, there will be three more events.........but lets say that's wrong, we know for SURE we're getting at LEAST one more event, and to get 25 points you just need to get the pass for one more event to earn 25 points by doing the prestige point missions
Remember, every event = 25 prestige points via missions if you get the pass.
So no worries, you'll be able to do it!
Now this is me guessing but looking at the calendar I'm thinking after this event we're possibly going to get the new ADC leaked, with her will come a line of skins. I'm going to ASSUME it's Star Guardians........however my problem with that theory is new hero releases lately have come with skins tied to an event.....we know Star Guardians isn't going to be an event, that means we're either getting a surprise skin line with an event next month, or SG is coming in September and the new champ is either getting a skin not tied to an event, or will be revealed in October with an event.
The more likely scenario in my mind is SG is September, new hero announcement is the very end of September, or early October, and her skin will be part of whatever line is coming with the Worlds/Halloween event.
Either way, major kudos to League for packing so much content into this year/Season!! :D