"This whole thing has been confusing as the information my client originally provided has proven to be somewhat inaccurate."

Amen to that. It's unusual (but not unheard of) for an operated well to accept partnership treatment, rather than to elect out of it. It's *very* unusual for all of someone's operated wells to be using partnership treatment. And it's pretty unusual for the well-level partnership to not either dissolve, or (more likely) be the asset that was sold when the well sold. So my guess is that you're still not getting all the facts, and that your client doesn't actually know all the facts. Any chance you can talk to the trust officer who handles the trust for the Trust Company, or to the CPA who prepared the trust's 1041? Usually if the Trust Company will hold / administer mineral interests, they have an in-house person who is pretty familiar with the tax and title issues.

With only the information currently in evidence, I agree with your conclusion. Here's some sample math:
The whole well is worth $1,000 at DOD, as evidenced by the Purchase and Sale Agreement (PSA is O&G lingo for the sale contract). It's the only asset of the operating partnership, which therefore also has a FMV of $1,000 at DOD. The decedent owned a 1% interest, worth $10.

The trust's inherited stepped-up basis in the partnership is $10. The well sells, and the trust gets $10 of taxable gain (which increases basis to $20), and $10 of cash (which decreases basis back to $10). The trust has $10 of cash, which carries out $5 of DNI when each beneficiary gets $5 of cash. The trust maybe also distributed the partnership interests (which don't carry out any DNI because there's no DNI left), and each beneficiary gets a partnership interest with an outside basis of $5 and a FMV approximating zero. When the partnership terminates, each beneficiary will have a $5 capital loss on termination.

Add a bunch of zeros, and you get the unpleasant result of a massive slug of taxable income, and a massive slug of long-term capital loss. If you can manage to have both the sale and the termination of the partnership in the same calendar year, and the taxable income is capital gain (as opposed to 1254 gain on recapture of depletion and IDCs), they'll offset and it's a less ugly answer. But most of the time, either the timing difference or the ordinary vs capital issue gives you a lousy tax answer. Which is why 754 elections are a thing, and why the election out of partnership treatment is a thing. But not things that your guy has a bit of control over, alas.