Oh look it's another doomsaying thread.
First of all, dying is not the word you're looking for. "Plateau'd" is the word you're looking for. League gains/loses players at a rate that is either not worth reporting (1% increases is nothing to boast about), is equal or basically even or a decline. However, that's not "dying". That's just hitting your peak. WoW had the same scenario in 2008-2009 when it peaked with Wrath. That game is still around today with about half as many subs as it used to have. Hell, check out DoTA2. The game has an average of just over 600,000 players on Steamcharts and it only just broke 13 million unique logins in the last month. It's extremely unlikely it'll ever get higher.
On the topic of DQ: Guess what, it's probably fine for most people. Can there be less ranked players? Sure, but your average player honestly doesn't give a damn. They don't have a dog in this fight. Readding solo queue won't do much other than maybe make some people stop complaining about it. (Hell, if anything it probably brought more players in despite a drop in ranked play because you can get roles you specifically want in norms.)
Queue times are also not the real problem here because you're selecting by role. It's MUCH easier to get people into a game when there are 5 randoms all fighting for who gets to be mid than it is for finding 2 people to fill this and that role specifically. Remember team builder? Same exact issue with queue times. Only instead of going through champ select you looked through each character to figure out what you wanted to put up with.
Twitch is incorrect as well. There are less overall viewers because there's more overall to watch. There's also an increase in vods and like triple the amount of games. 200k viewers for 4 games vs. 120k viewers for 12 games. Also streamers/players saying they'll quit is nothing new.
You're also comparing incredibly broad and generic claims. "Many players" "Lots of people" etc. The only real proof is that there hasn't been any player statistics posted since 2014 or so and the whole PC Bang thing. For all we know, maybe us 100 people are the last people playing ever. Maybe the rumors of death are greatly exaggerated.
Finally: You can't save a game when it's in decline. You can triage and you can entice new players/bring old ones back (Which will happen whenever Riot has a new champ, the new client or a game mode) but you're not going to "save" the game. League peaked and Riot can basically do whatever they want. They're not going to magically save the game and make it more popular than it ever was before.