what are you imagining, what is the question for?
I ask because, if its in solution, then I doubt it degrades under 100c, because extended boiling does not diminish the potency of harmala-containing brews. Now, if you have evaporated all the water and have 'dry' harmaline acetate (which I imagine must be a goo, but I dont know), then I really have no idea. I also dont know if it 'decomposes' into anything inactive or if the acetic acid simply evaporates off and harmaline freebase stays.
I may be wrong but I doubt anybody knows the exact temperature of harmaline acetate 'decomposition', so I guess its up to us to start testing it somehow