It depends, in part, on the terms of the installment agreement and the nature and terms of the subsequent agreement regarding collectibility. Presumably, the tax may be collected by levy within 10 years after the assessment or pursuant to the terms of the installment agreement, unless the subquent agreement alters the time limitations.
Relief is available in some situations in the form of an offer in compromise.
A compromise of a tax liability may be entered into when collection of the full liability would create economice hardship. The IRS may accept an offer in compromise to settle an unpaid tax account for less than the full amount of the balance due. Acceptance of an offer in compromise on such grounds takes into consideration all the facts and circumstances. Other factors are inability to meet basic living expenses if assets are liquidated, and inability to borrow against the equity in assets and adverse consequences resulting from a levy on the assets. These include lack of history of noncompliance with the tax laws and lack of deliberate actions to avoid the payment of taxes.