Don't worry, your work isn't completely lost. You have only lost the virtual table you explicitly dropped and the operation immediately prior to the dropped table. The the table you want is either in your hidden or temporary table list. In addition, you may also find it as part of another active table's dataflow graph.
The only scenarios where a dataflow graph would disappear are:
1. if the previous table were used to produce another active table in your worksheet in which case it would be a temporary table
2. if you explicitly used "Hide Table" to prevent it from displaying a dataflow graph.
Take a look and let me know if you have any additional questions about this!