I'm happy for Jadon Sancho's decision honestly. Because he had no future at Manchester United with Erik ten Hag because of the problems between them. It is great to see him back at Dortmund as he was playing really amazing there before. Terzic must also be happy to have him. Their season in the Bundesliga hasn't been going on well for them.
Everyone must feel happy to see Jadon Sancho joining Dortmund again. He deserves to play in Dortmund where he got a big support and he got a chance to grow to be a top player. I'm sure Jadon Sancho will play again with his best performance. Sure, he won't have a future if he stays in Man United, especially if Ten Hag is still the coach. Ten Hag doesn't give him the chance to play, Jadon Sancho spent his time in the bench. Now, he will have the chance to develop again with Dortmund.Sancho could really make a good impact on the performance of the team here. With his contribution I hope to see Dortmund back in top four at some point. This would save Terzic from the threat of getting sacked at the same time. 
It is too early to claim Jadon Sancho to give good impact. But I'm sure Jadon Sancho will contribute well if he gets enough chance to play. Jadon Sancho must play more often, so he can perform again as previously. Dortmund must know how to treat him well. 