Amanda--Please list what state you are from, because if what you are writing is correct, the rules you list do not apply to all states. Anyone thinking about disbanding needs to check their local unit bylaws. Incorporation is generally done not through the PTA, but through a State Corporation Commission or some other such state government office. Also, in my state (VA) the dissolution provision reads as follows:
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Upon the dissolution of this organization, after paying or adequately providing for the debts and obligations of the organization, the remaining assets shall be distributed to one (1) or more non-profit funds, foundations, or organizations which have established their tax exempt status under Section 501(c)(3) of the Internal Revenue Code.
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I believe this is fairly standard language. Clearly, this does not mean that the leftover money must go back to the State PTA. The members of the local PTA unit can vote to decide what organization gets their leftover money.
Not only will there be IRS issues but you must turn over any and all leftover funds to the PTA State Board. You still have to do all the IRS Tax forms and any and all documentation needs to be sent confirming the dissolution, because you are incorporated by that States PTA, Therefore you pay Dues to that State and that through the State's Incorporation process the monies become that of the State PTA's.
I would just like to point out that you DID agree to the PTA's bylaws when your unit chartered so in essence you did "sign" an agreement when you became a member of PTA and chartered your organization under their umbrella.
Further, the EIN you received from the IRS was likely via the umbrella from your state's PTA with which you obtained 501(c)(3) status. I'm sure you will be professional enough to follow the bylaws your unit agreed to when they became a PTA and give notice of disbandment to your state PTA so that they can remove your EIN from their umbrella. The IRS will essentially "close out" that EIN and you will have to get a new one. It would sure suck for you if you continue to use the PTA's EIN only to have it revoked and you lose out on valuable donations because you didn't follow the rules.
Technically, as a PTA you likely don't have your own 501c3 status. Most PTAs get their 501c3 through their affiliation with the state PTA (it's akin to an umbrella 501c3). If that's your situation, then when you leave PTA (or when PTA declares you no longer affiliated, if you just let things wither) you no longer are a 501c3.
What you likely have is an EIN (employee ID number) from the IRS. And you can keep that. But that's not the same as a 501c3 designation.
Even given that, you're correct that there are basically two ways to no longer be a PTA. 1 = Go through the prescribed bylaws steps for dissolution; 2 = Basically let the existing PTA go dark (by, for example, not having elections and not having a membership drive for next year). In that second case, at soe point the state PTA will declare your local PTA not in good standing and sometime after that will consider your PTA done.
Most (but not all) PTOs do wind up getting their own 501c3 status, but that's not particularly difficult to get.