Yes there have been cadets " let go " or fired if you will, pre and post line check and a couple up to the end of the first 8 months, prior to being offered a flexi crew contract. I don't know what happened after they left, the arrangement I'm sure was between them and CTC.
As has been previously mentioned forget about the "bond", all it is is the training costs CTC require for the course, if you end up on flex crew you don't see any bond repayment. The hourly rate is all you get, hope that's clear enough for anyone wondering.