re: How long does buttercream stay fresh

I’ve had to make a decision to just go with it and hope for the best but have had a light bulb moment when making the buttercream. The cake is a take an tiramasu; so ive made a coffee cake, put some marshland wine in the sugar syrup and just added marshland to the buttercream!! My logic is that the wine will help to “preserve” the butter. I’ve not added any other liquid. ….

Any thoughts?