> Is there any likelihood of an acquirer being interested in purchasing the product but not its developers?
At the very least you will be expected to stick around for documentation and gradual hand-over. This may well be the only card in your hand during a negotiation, or it may not be, depending on the circumstances and your relationship to the people transacting the acquisition.
I have to point out though your assumption is that the product is the key asset a buyer will be interested in. Is this the intention of the founders as well? Because counter-intuitive as it may seem, the new company might be more interested in the people who sold this product than the thing itself. Do what you can to find out more.
> Assuming I do stick it out as an acquihire, what's the likelihood I'd be allowed to remain in charge of my product vs having to execute on someone else's vision?
That depends totally on your relationship with your new employer and the structure and politics of the new company. Best case, you'll move up the ladder there. Worst case, they want to get rid of you as soon as possible. Average case: in a year they regret the acquisition, because they realized they'll never make back the money they paid for it. If you do like it there, it might make sense to move onto a more important product in their core portfolio before the acquisition hangover hits them.
> how do I best stand up for my own interests here, without being the asshole that ruins the deal for everyone?
Be friendly, exude an aura of confidence and competence, but don't be a roadblock. Find out what the decision makers want (first at your current company, then at the new one) and help them achieve their goals. The risk is still you'll be left at the side of the road, but then again, that's always a risk.