Whipped egg white snack texture and preservation I am trying to make whipped marshmallow egg white snacks. I would like the end texture to be between heavy whipped topping and a marshmallow and preserve flavors and texture for 5-7 days.

I have been following the following recipe.

However I ended up with an outcome which was more like a heavy whipped cream as opposed to a gooey like marshmallow cream snack, which is what is desired. Also, dipping it in the chocolate made it fall apart.  

Note, the sugar syrup color and thickness was slightly lighter than what was in the video. 

Would adding gelatin be a good idea for the desired outcome, if so at what point should it be added and at what ratio?

Adding cocoa powder for a chocolate flavored whipping caused the density of the cream to undesirably reduce.

What is the best way to preserve this to ensure it lasts 5-7 days?
The treat you are describing I believe is a meringue. These little guys are tricky to get right the first time, as it is all about how long you cook them for and how finely you whip the egg white mixture. What I like to do is add a bit of lemon zest on each one. Not only does it enhance the vanilla flavour (if you're using it), but it also serves to tell you when the meringue is just about ready (goes brown/near black). I have never tried adding gelatin but I don't suppose that would turn out well. 

My suggestion: Cook the meringues at about 160-180 degrees celsius, checking on them every 5-10 minutes. Press your finger into one of them if you feel they are ready (the sacrifice of one for the survival of many, I know) and keep repeating this until you feel you have reached your desired texture. The beautiful thing about them is: you can cook them a little to leave them marshmallow-ey or you can cook them into crumbly, crunchy, snacks. 

As for how long they last, meringue tend to last about two weeks without a significant change in quality in an airtight, sealed container.

Quick Tip: To keep them soft in texture, let them cool slowly in the oven with the door ajar. 

Good Luck!