For those wondering if any of the players drafted yesterday or today will return, last year 309 of 312 players (99%) chosen in the first 10 rounds signed pro contracts.
The new MLB draft rules make it to where clubs almost have to sign the players they draft in the first 10 rounds, otherwise they will face financial penalties. In most cases I think agreements, or at least understandings, are pretty much in place before the draft picks are made.