As long as you want.
PicDrop never interferes with your data. This means: we do not change or delete any data unless you explicitly request us to do so. All galleries remain online until you delete them yourself when you no longer need them.
This also holds true for our free plan: all your previously created galleries and all uploaded pictures will remain. However, if the total amount of data or the number of uploaded images exceeds the amount included in your plan, the images or galleries can no longer be downloaded nor accessed by third parties, i.e. your clients.