What he said is familiar with what I am familiar with too. If you fail to honor your agreement, the agreement is void. They can levy your account or they can agree to allow you catch up the following month and continue paying monthly - it is up to them. They can also put you in jail for tax evasion. What are they "likely" to do? It depends on a number of things - how much you owe, why you failed to pay, whether you tried to get away with not paying - in other words, without knowing your circumstances, I can't guess what they will do. A tax attorney can probably help you but, it sounds like you can't afford an attorney either.
Certified Paralegal, with 25+ years' experience.