Stay and play in Europe. I vote for Croatia; BA flies from ZAG to LHR so you can easily get from there to Nigeria.
Would it be possible to for you and your DH to pack one suitcase with vacation clothes and the other with your work clothes. That way your DH can fly home with them and you wont have to tote them to Nigeria.
Stay! Slovenia is one of my favorite places and you don't mind traveling alone so I would definitely do that. Plus will your work pay for your ticket if you stay?
I haven't been here, but in researching our upcoming Italy trip, I discovered this place. I was just looking for wine tours, but it has great reviews. fattoriapoggioalloro.com/?lang=en
I think I would stay. That way you're not in transit and you get to check out Slovenia. I know having less miles would stink but it would be nice to see somewhere new.