I don't use promoted listings so it will likely vary for those that do. But I have always found when I get back into regular listing my sales increase within a few weeks to what they where before. It will be different on so many levels trying to compare each seller as everyone sells different things though.

New listings will help with sales but they do not account for the majority of my sales as it is the older items that tend to start moving again. So as you can see this won't help a new seller as they won't have the listing numbers needed to keep sales regular.

Most new sellers tend to sell items from around the home and as such get a burst of sales until all the popular and well priced items have sold and then everything stops.