yes, they have the right to extend but forcing participants and threatening them that their stakes will be forfeited is a huge red flag.
It is a red flag for me I don't know how long they want to extend it, they should have announced before the start of the campaign that they want the campaign to run a total of 15 months or more, there is a possibility that they will keep extending it until bounty hunters lose the motivation and left so they will have no bounty to pay to those who choose to leave.