Yes!! You keep the deviation bank. Here is the process to get it restored.
After the start date of the trip you were bumped from
go into your expense report in the first (deviation bank) section and click on the "Add Missing Travel Bank Record" button. The pop up window will give you the option to restore your bank. Just use the pull down and select Bumped For Training (BFT).
As mentioned above, you will need info off of the original pairing including pairing number, date, the scheduled deadhead airline and flight number and the bank value.
You'll get a crew notification within a day or so and the bank will reappear in your travel claim within another day.
Only trick is that you can not do this until the date of the original pairing.