I honestly don't think Buffalo will be fighting for a playoff spot next year. I doubt a single player can have such an impact, especially when 18 year old defenceman in general rarely make a big impact.
No need to give up though. Dahlin changes the whole outlook on the future.
Depends on the moves Botts makes as it's not going to be just one player. Botterill has talked about Guhle, Ullmark, and Mittelstadt improving the team next season so I would assume they're on the starting roster.
He also talked about needing to bring in speedy wingers so maybe he targets players like Hagelin, Grabner, or someone like Miles Wood. Whoever he brings in should be a huge improvement to the team they want to build compared to Pominville, Pouliot, and Girgensons as top 6 wingers. People always talk about how its easier to get wingers...so hopefully it's true as its the Sabres biggest weakness right now.
Guhle was better than pretty much everyone other than maybe Scandella on the left side but Guhle only played 18 games.
Pilut>Beaulieu/McCabe.
Mittelstadt >Larsson and Josefson as the 3C but Mittelstadt only played 6 games.
Dahlin should be a top 4 defenseman on the team even in his draft season.
Ullmark + some other goalie should be > Lehner/TheChad as they were downright useless.
Every single team in the last 5 years that has won the lottery has made the playoffs the next year or the following year, obviously every circumstance is different..but we shall see. Either way I don't see this team in the bottom 5 at least.