Beyond contract negotiations and the selling of international distribution deals and or rights, what does the literary agent do after the book has hit the shelves? In other words: after the marketing machine of the publishing company has shifted towards another writer’s book, how actively involved is the lit agent in maintaining some momentum in keeping the public’s interest in the work – as in readings, signings, panels at festivals, interviews and so forth.
What you're describing is a publicist's job more than an agent's - we don't tend to have expertise in organising signings and getting authors onto panels at festivals. We have expertise in giving you editorial advice, getting you published and keeping you writing; we provide advice on writing and other stuff, usually, that has nothing to do with writing but which may be stopping you writing; we're here to sort out any problems that may arise with you getting interviews etc, but we can't organise them. We may be able to rely on our contacts to get you a foot in the door but, again, we can't organise them.
There's a good reason for this, beyond the fact that it's not our core competency: it takes a lot of work to find you a publisher, to negotiate a contract and to handle foreign rights. In most cases, it takes many more hours than the commission actually covers. Once the book is out, we'll liaise with your publicist if the need arises (although in my experience most book publicists do just fine), and handle anything else that needs handling, but if we added publicity to our list of duties, we'd only be able to take on about two clients a year. As far as I know, there's only one agency in the US that provides those sorts of services - Folio - but the US is in a different stratosphere.