What is the possiblity of rainforests being restored after human interference - succession?

It'll take time, but nature will take it's course. It really depends on how badly we've damaged them. If we've burned them down, then primary succession will have to occur first (pioneer species come in and the ecosystem slowly grows back from there). If we've cut much of it down but there's still organic matter secondary succession will take place and it'll take less time. However, in many cases, rain forests have been cleared for farmland, turning the soil into very poor quality silt.. It'll take quite a while for that to grow back.