They should get prospects back. It’s really difficult to get contributing major leaguers at the deadline, since any team you’re dealing with expects those players to stay and, well, contribute. Cherington tried tjis in 2014, dealing Lester and Lackey and hetting back Allen Craig, Yoenis Cespedes and Joe Kelly. Craig was just a bad contract that did nothing in Boston. Cespedes was later flipped for Rick Porcello that off-season. Only Kelly stuck around. Selling off your two best pitchers should have yielded much more.
Get prospects. Deal them in December/January when more teams will be in position to make deals with a better variety of targets…