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 files will remain in your account. However, if the total amount of files or the number of galleries exceeds the amount included in your plan, the files or galleries can no longer be downloaded nor accessed by third parties, i.e. your clients.