I say send something. It couldn't hurt! Your previous boss may be smearing your rep, but I think it says a lot that they still asked you to stick around for an "as-needed" basis. Get your foot in the door anyway you can and let them know you are available for as much as they'll give you, including full time. If you help out and work with them in some capacity, they'll see your last boss was a lying sack and maybe hire you full time!