Your probation conditions may be extended. It all depends on how close (or distant) you are to completing it. If you had done 9 weekends out of 10, they’ll usually just give you a few weeks to finish. If you are half way through, then they’ll probably extend your probation conditions for another six months to a year.
If you have completely blown them off, you are looking at a weekend or two in jail, plus extended probation, plus increased community service. And i you are an adult, they won’t put you in juvie, you’ll be in the grown up jail with all those nice people and no privacy.