I don't know how exactly SRB2db works since I use the normal one but if it's just because your file is corrupted than there's one easy way.
Those wadeditors usually keep storing filebackups into the directory the main file is located. Just search for files named (if your wad is called "test.wad" for example):
test.wad.backup1 or test.wad.backup2 or test.wad.backup3...
test.wad.001.bak or test.wad.002.bak or test.wad.003.bak ...
Then take the newest one, copy it, rename it to test.wad thus changing the data type and voilà, your file is restored.
;)
Edit: Whoopsy, Violo was faster. ^^