There's no way Vettel was letting him in, nor would Ferrari go for 2 competitive drivers, even promoting Leclerc is a bold move for them. Kimi has been the perfect no 2 driver really.
Renault are in the best shape to make the next jump forwards, Haas and Force India aren't awful teams, but the former is still very new and making mistakes, and the latters financial issues will have affected development for next year. McLaren claiming they nearly signed him is the biggest joke of the year (but cheers for confirming Alonso is off guys, we know you can't afford both). Sauber should come back strong now they are basically Ferrari B, but then thats not what Ricc wants. Sadly Williams are really out of the loop.
The steps forward Renault have made in 2 years are pretty impressive, and they've a championship winning pedigree to prove they take the sport seriously. Also in Hulkenberg he's got a really talented teammate to push him to his limits.
Hopefully RB give Sainz the seat, really likeable guy (pretty much everyone in the paddock hates Gasly because he's arrogant even by Frenchman standards), and a great driver too.