Good trade. Moniak has no future here with Marsh on board, Sanchez is part of a group of young OFs in A ball who are 3 years away if ever - he has upside but he's still a long shot.
I think Syndergard is a candidate for an extension if he shows enough, FB up to 94 (down from 97) but first season after TJ surgery. His biggest fall-off has been his changeup, which he throws too hard given the decline in FB velocity - that's something a good pitching coach can work on, doesn't require a major adjustment.
He's only 30, even if he never gets above 95 again, he has 5 pitches and is a candidate to improve as he learns to pitch with less velo, and would be a good bet for a back of the rotation starter on say a 3 year deal.
This takes the pressure off Falter and Sanchez to fill the #5 hole, they'll still get some spot starts to rest the top guys, but I think Falter is maybe a year away from pushing for a rotation slot, he's upped his velo a little, but needs to bring it more consistently.