How to preserve herbal syrup or herbs that will be used to make syrup? I want to preserve my windowsill herbs before the plants die back, and my idea is to make herbal syrups for lemonades or cocktails. (Possibly even meat sauces.) The method I'll use is a cold, dry maceration - bruising herbs in sugar and leaving them in the fridge for a day or two for the sugar to absorb the flavour, and only using enough heat to dissolve the sugar later.

While this makes for superior flavour, the lack of boiling makes this prone to spoiling - my previous batches had weird gunk floating in them eventually.

I've read in other questions that freezing herbs alone can diminish their flavours. Can I, say freeze 1:1 or 2:1 syrup without this happening as well? Or maybe just freeze the sugar-herb mush once it's done macerating? (I'm hoping the flavours being bound in the sugar might help.)
Remember that whatever method of preservation you use you will always lose some flavor, there's no way to keep it all. 

If you want to make a syrup for long term preservation then freezing them is your best bet unless you want to add preservatives which you don't really need to do if you have a freezer. A smart way to do it would be to pour the syrups into ice cube trays, then once frozen pop them out into zip lock freezer bags so you can use the trays for other things, and keep the ice from sublimating. I'm in favor of straining the syrup first, that way the cubes are ready as soon as they come out of the freezer. 

Depending on the herb it may be more efficient to simply freeze the herbs directly. Thick herbs like sage, rosemary and thyme will do just fine while others like basil and parsley will turn to mush and you'll lose flavor. 

Have you considered drying them? It's not hard to do, and there's plenty of how-tos out there, may be the best solution for thin herbs.