Severus did come back of course, though he remained on the peripheries of the conversations flowing around Hermione. It goes without saying that Minerva insisted on being left to deal with the culprit herself. She felt she could get the answers far more easily than Severus, though it was mainly her observation that whilst Severus had been acquitted of one murder, a second would be 'careless.'
Minerva was right of course, and in an exclusive expose detailed by The Quibbler, Lavender Weasley (nee Brown) was brought to justice by her old Head of House under the guise of a job interview. Mind you, the extra strength Veritaserum brewed especially for the occasion by Severus helped immensely.
Severus formally handed over Hermione's care and recovery to Poppy Pomfrey on the same afternoon that he had cured her. He was very circumspect about his reasons, but with references from both Poppy and Minerva, he was able to secure a senior position at St Mungo's almost immediately. He continues to call Hogwarts home, as does Hermione.
Severus gently explained to Hermione after she had healed fully how he had finally deduced the person who had cursed her so callously. Her memories of honeysuckle acted as a trigger of sorts, though without Hermione's honesty, he would never had the made the connection between an overpowering scent and a cloying, malicious person.
Hermione recovered quickly physically, but it took far longer for her to gain some sense of her own self after so long a seclusion from the world. She is currently studying hard in an attempt to be the oldest student to complete her N.E.W.T.S. She has no idea what to do as a career, but Neville Longbottom has already offered her an apprenticeship in his Herbology supply business. Severus, naturally thinks it's an offer that is too good to refuse. The thought of discounted ingredients from the best supplier in England means nothing of course.
Minerva and Poppy are happily playing matchmaker-and succeeding admirably.
Original Prompt: Hermione has been cursed. Rather than harm her physically, her attacker went after her mind. She's now paranoid and terrified of everything, and refuses to leave her home. Since the curse is dark in nature, Snape is sent in to figure out a counter-curse. For reasons he can't figure out, Hermione only feels safe with him. Can Snape remove the curse? Who cursed Hermione and why? H/C and romance with a happy ending, please.