He doesn't come back as a main character but he makes a couple of guest appearances after season 4. Once in season 5 and again near the end of Buffy in season 7. He makes a phone call (but you don't see him) to Buffy in season 6.
posted over a year ago
I just want to add that a big reason for this is because Angel has his own series beginning with season 4, and it is totally awesome (The Shanshus Are Coming, so check Angel out!) link