It remains to be seen. It's impossible to really know the impact of rushing prospects to the NHL. Down the road it may end up being great for him, or it could backfire badly which is why some teams don't do it as it's not worth the risk. Look at McCarron, he had 20 pts in 21 games to start his pro career in the AHL, gets called up later on and ever since he hasn't been anywhere near the same player. Not saying it's directly related, just that I wish this management team would take more caution with rushing under 22 year olds to the NHL, especially our 1st round picks.
Sergachev only played 3 games in the nhl, so he was not rushed at all. Practicing and playing at an nhl level for a month will only make him better and accelerate his development.
McCarron wasn't rushed either. He was called up in the nhl like several other players when the season was already lost. McCarron also played really well this training camp + preseason, so I doubt last year 20 game stint had a negative effect on him. If anything it was positive.
Both Sergachev and McCarron have started slow their season, and I think one of the reason of it is that they thought they were going to be in the nhl right now. McCarron would have started in the nhl this season, but we did not have a spot available. Sergachev said he was shocked when they told him he was sent down, he was expecting to play at least a couple more games, and maybe even stay for the season. It will take them some time to get over it, but they will soon start playing to their potential. McCarron already looks a lot better now than at the start of the season. A few more games for Sergachev, and I think he will return to looking good after that.
Also, a guy who I would say was rushed is De La Rose.