If you eat cake and chocolate such that you say mezonot, eat cake, say shehakol and eat chocolate, then can you say al hamichiya on the cake when you have finished the cake, and continue eating the chocolate, and then say borei nefashot when you are done with the chocolate, or do you have to say them together when you finish eating altogether?
In other words, can you partially finish eating but not totally finish?

I would say yes but I can't prove it.

I have been wondering this for awhile...

I learned that as long as I have in mind, before I make my al hamichya, that I'm not finished my chocolate, I can continue eating the chocolate and make the borei nefashos when I'm done.

Why not just wait until you're finished with everything and say one after-blessing?

Why not just never eat anything except during a bread meal? Who knows why. Somebody wants to. Maybe Nechama Dina is eating a snack in Prospect Park with Sarah Draizel, and Sarah Draizel has to leave because she has to get her daughter to the mall where she's handing out shabbos candles, but Nechama Dina doesn't have an al hamichiya on her - she left her Chitas in her car - so Nechama Dina wants to say al hamichiya before Sarah Draizel leaves but isn't finished her chocolate bar yet.

I have that with my kids. I just hope they don’t forget. I’d go piece meal.

Let me get this straight, Person A and Person B are eating together. Both have said "bore mine mezonoth." Person A needs to leave, but person B hasn't finished eating. Somehow, Person B is incapable of saying the after-bessing on her own!? Since she already said the blessing and ate mezonoth, why does it matter if she doesn't have any more on her?

Why not? Its not a meal but rather a snack.

hmm...I think I messed up the example. But regardless, the question stands: Can I say al hamichiya but continue to eat my chocolate bar and say borei nefashot when I finish the chocolate bar?
To me, the theoretical problem is that once I say al hamichiya, I have declared an end to my eating session. which may possibly mean I need to say borei nefashot as well. I've made a hefsek, just like when I wash mayim acharonim. and if i want to keep eating the chocolate bar, I may even need a new shehakol.
now I'm not saying that's the case. I'm asking the question.

Just have in mind that the after-blessing on the cake is not exempting the chocolate.

It can't, anyway.

The after-blessin on mezonoth can't exempt the after-blessing on something "shehakkol?"

As far as I know, to the best of my limited understanding, as a general rule not. However, that's not entirely true because there are opinions that if let's say you say al ha-eitz, it can exempt an apple which would mean that in theory, if you ate dates and were saying al ha-eitz, if you also hold chocolate is eitz [and not shehakol] then yeah, maybe in theory. But al hamichiya exempting chocolate for which you said shehakol? I don't think so, not to the best of my limited understanding.

Why, its not considered a seuda as its mezonos.
This is all a case when you didn't have in mind to maybe continue eat the chocolate after the cake

There is actually a similar situation le'maase.

On the second night of RH, minhag Chabad is to eat a new fruit right after kidush to alleviate potential shechyanu issues. And an after brocha is made after the fruit before washing (to alleviate other problems), but NOT over the wine (presumably because it would interfere with kidush b'makom seuda).