If the IRS and you negotiate a payment plan for back taxes, can you still file for Chapter 7 bankruptcy down the road?

As long as you are only on a payment plan, and not an offer in compromise, the time frames for discharging taxes on measured income are not extended. The only way to be absolutely sure of the earliest possible date to discharge taxes is to obtain a copy of your tax transcript and use the dates of filing and assessment to calculate the date beyond which the taxes are dischargeable. Either an offer in compromise, or an extension of time to assess are matters which delay the date of dischargeability.