[moonka]

Not if you go through the seatpost. Seatposts are pretty easy to replace.

[mankyd]

Except the lower of bar of the bike would still have the (now) 2 pieces of the seat post attached to them and wouldn't be able to close shut.

A committed thief could, of course, take it from there and have time to remove the remains of the seat post at a more convenient time and place.