Hi Tash :-)
I haven't had my test or cure yet but from what I've read on this forum Lletz has an extremely high success rate of around 80 - 95% so the odds are definitely in your favour. I'm due my test of cure in just over a week (my history is on my signature) and my worries and nightmares seem to have started all over again - it's such a scary thought that it could return. I've been taking lots of supplements and trying to stay healthy, so I can at least feel as though I'm doing something. It helps to avoid stress too, but that's so much easier said than done!
To answer your question though I think it would depend on the severity of the abnormalities whether or not you would have to have a Lletz again if they returned - if they were borderline they may just keep a closer eye on you, as there's a good chance the cell changes would regress.
When I've spoken to friends about this, most of them at least know someone who's been treated for abnormal cells, and from what I've heard they've all been fine. A lady I work with has had two Lletz but has had clear smears for several years now.
Try to stay positive and remember that you're in the system now so they're keeping a close eye on you :-)