The one pokemon I'll be very disappointed without is Reuniclus, that's the one that got me hyped for black and white and I drew that the day it was revealed. I don't think I have much to worry about considering it's been in X, Y, Sun, Moon but it hasn't been confirmed yet.
Some of the pokemon I never want to see gone are Chinchou and Lanturn (confirmed) Phanpy and Donphan, Wooper and Quagsire (confirmed), Houndour and Houndoom, Sneasel and Weavile (confirmed, thank fuck), Slakoth (I literally don't care about the others), Mudkip, Mawile, Spoink and Grumpig, Spheal Sealeo and Walrein, Piplup, Shinx Luxio and Luxray, Cranidos and Rampardos, Buizel and Floatzel, Woobat and Swoobat, Cottonee and Whimsicott, Petilil and Liligant, Sandile Krokorok and Krookodile, Litwick Lampent and Chandelure, Larvesta and Volcarona, Skiddo and Gogoat, Furfrou, helioptile and Heliolisk, Tyrynt and Tyrantrum, Amaura and Aurorus, mimikyu (confirmed).
Like Bidoof is fucked, Luvdisk and Alomomola are too.