After my departing (meta tēn aphixin mou). Not his death, but his departure from them. From aphikneomai and usually meant arrival, but departure in Herodotus IX. 17, 76 as here.
Grievous wolves (lukoi bareis). Bareis is heavy, rapacious, harsh. Jesus had already so described false teachers who would raven the fold (Joh 10:12). Whether Paul had in mind the Judaizers who had given him so much trouble in Antioch, Jerusalem, Galatia, Corinth or the Gnostics the shadow of whose coming he already foresaw is not perfectly clear. But it will not be many years before Epaphras will come to Rome from Colossae with news of the new peril there (Epistle to the Colossians). In writing to Timothy (1Ti 1:20) Paul will warn him against some who have already made shipwreck of their faith. In Rev 2:2 John will represent Jesus as describing false apostles in Ephesus.
Not sparing the flock (mē pheidomenoi tou poimniou). Litotes again as so often in Acts. Sparing the flock was not the fashion of wolves. Jesus sent the seventy as lambs in the midst of wolves (Luk 10:3). In the Sermon on the Mount Jesus had pictured the false prophets who would come as ravening wolves in sheep’s clothing (Mat 7:15).